Implement XEP-0167: Jingle RTP Sessions multiplexing

[melvo]

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
• [x] Add unit tests
• [x] Format the code: Run clang-format -i src/<edited-file(s)> tests/<edited-file(s)>

[codecov[bot]]

Codecov Report

Base: 68.42% // Head: 68.47% // Increases project coverage by +0.04% :tada:

Coverage data is based on head (fe975b8) compared to base (9f474d2). Patch coverage: 100.00% of modified lines in pull request are covered.

:exclamation: Current head fe975b8 differs from pull request most recent head 7455a6c. Consider uploading reports for the commit 7455a6c to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #467 +/- ## ========================================== + Coverage 68.42% 68.47% +0.04% ========================================== Files 279 279 Lines 24306 24333 +27 ========================================== + Hits 16631 16661 +30 + Misses 7675 7672 -3 ``` | [Impacted Files](https://codecov.io/gh/qxmpp-project/qxmpp/pull/467?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/QXmppJingleIq.h](https://codecov.io/gh/qxmpp-project/qxmpp/pull/467/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2Jhc2UvUVhtcHBKaW5nbGVJcS5o) | `100.00% <ø> (ø)` | | | [src/base/QXmppJingleIq.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/467/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2Jhc2UvUVhtcHBKaW5nbGVJcS5jcHA=) | `86.80% <100.00%> (+0.70%)` | :arrow_up: | | [tests/qxmppjingleiq/tst\_qxmppjingleiq.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/467/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-dGVzdHMvcXhtcHBqaW5nbGVpcS90c3RfcXhtcHBqaW5nbGVpcS5jcHA=) | `100.00% <100.00%> (ø)` | | | [tests/qxmppomemodata/tst\_qxmppomemodata.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/467/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-dGVzdHMvcXhtcHBvbWVtb2RhdGEvdHN0X3F4bXBwb21lbW9kYXRhLmNwcA==) | `98.24% <0.00%> (-0.01%)` | :arrow_down: | 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)

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