Add convenience data retrieval method to QXmppBitsOfBinaryDataList

[jbruechert]

PR check list:

• [x] Document your code
• [x] Add \since QXmpp 1.X, QXMPP_EXPORT
• [x] Fix doxygen warnings (see log when building with -DBUILD_DOCUMENTATION=ON)
• [x] Update doc/doap.xml
• [ ] Add unit tests
• [ ] Format the code: Run clang-format -i src/<edited-file(s)> tests/<edited-file(s)>

[codecov[bot]]

Codecov Report

Base: 68.60% // Head: 68.24% // Decreases project coverage by -0.36% :warning:

Coverage data is based on head (e62c02d) compared to base (f762f73). Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #475 +/- ## ========================================== - Coverage 68.60% 68.24% -0.37% ========================================== Files 283 293 +10 Lines 24571 25108 +537 ========================================== + Hits 16857 17134 +277 - Misses 7714 7974 +260 ``` | [Impacted Files](https://codecov.io/gh/qxmpp-project/qxmpp/pull/475?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project) | Coverage Δ | | |---|---|---| | [src/base/QXmppBitsOfBinaryData.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/475/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2Jhc2UvUVhtcHBCaXRzT2ZCaW5hcnlEYXRhLmNwcA==) | `90.90% <0.00%> (-9.10%)` | :arrow_down: | | [src/base/QXmppBitsOfBinaryDataList.h](https://codecov.io/gh/qxmpp-project/qxmpp/pull/475/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2Jhc2UvUVhtcHBCaXRzT2ZCaW5hcnlEYXRhTGlzdC5o) | `100.00% <ø> (ø)` | | | [src/base/QXmppFileShare.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/475/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2Jhc2UvUVhtcHBGaWxlU2hhcmUuY3Bw) | `45.33% <0.00%> (-16.94%)` | :arrow_down: | | [src/base/QXmppUtils.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/475/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2Jhc2UvUVhtcHBVdGlscy5jcHA=) | `81.98% <0.00%> (-4.69%)` | :arrow_down: | | [src/base/QXmppFileMetadata.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/475/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2Jhc2UvUVhtcHBGaWxlTWV0YWRhdGEuY3Bw) | `50.87% <0.00%> (-1.51%)` | :arrow_down: | | [src/client/QXmppFileEncryption.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/475/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2NsaWVudC9RWG1wcEZpbGVFbmNyeXB0aW9uLmNwcA==) | `67.44% <0.00%> (-1.07%)` | :arrow_down: | | [src/base/QXmppMessage.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/475/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2Jhc2UvUVhtcHBNZXNzYWdlLmNwcA==) | `98.31% <0.00%> (-0.55%)` | :arrow_down: | | [tests/qxmppmessage/tst\_qxmppmessage.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/475/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-dGVzdHMvcXhtcHBtZXNzYWdlL3RzdF9xeG1wcG1lc3NhZ2UuY3Bw) | `94.82% <0.00%> (-0.02%)` | :arrow_down: | | [src/base/QXmppError.h](https://codecov.io/gh/qxmpp-project/qxmpp/pull/475/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2Jhc2UvUVhtcHBFcnJvci5o) | `0.00% <0.00%> (ø)` | | | [src/base/QXmppError.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/475/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2Jhc2UvUVhtcHBFcnJvci5jcHA=) | `0.00% <0.00%> (ø)` | | | ... and [18 more](https://codecov.io/gh/qxmpp-project/qxmpp/pull/475/diff?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project) | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project)

:umbrella: View full report at Codecov.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.

[melvo]

@jbb There is a typo: It should be convenience :)