Add signature's dictionary entries on API (/ContactInfo, /Prop_AuthTime and /Prop_AuthType)

[eduperottoni]

Description of the changes

This PR adds some options that high level API doesn't support regarding to signature's dictionary entries. More specifically, adds support to coverage of the following signature entries, described in ISO-32000: /ContactInfo, /Prop_AuthTime and /Prop_AuthType.

Related to #307.

[MatthiasValvekens]

@eduperottoni Please also make the linter happy with isort --profile black --line-length 80 pyhanko pyhanko_tests and black -q -S --line-length 80 pyhanko pyhanko_tests

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (fc3d7d2) 98.76% compared to head (f258829) 98.76%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #314 +/- ## ======================================= Coverage 98.76% 98.76% ======================================= Files 104 104 Lines 14712 14730 +18 ======================================= + Hits 14530 14548 +18 Misses 182 182 ``` | [Flag](https://app.codecov.io/gh/MatthiasValvekens/pyHanko/pull/314/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matthias+Valvekens) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/MatthiasValvekens/pyHanko/pull/314/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matthias+Valvekens) | `98.76% <100.00%> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matthias+Valvekens#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files Changed](https://app.codecov.io/gh/MatthiasValvekens/pyHanko/pull/314?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matthias+Valvekens) | Coverage Δ | | |---|---|---| | [pyhanko/cli/commands/signing/\_\_init\_\_.py](https://app.codecov.io/gh/MatthiasValvekens/pyHanko/pull/314?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matthias+Valvekens#diff-cHloYW5rby9jbGkvY29tbWFuZHMvc2lnbmluZy9fX2luaXRfXy5weQ==) | `98.79% <100.00%> (+0.01%)` | :arrow_up: | | [pyhanko/sign/fields.py](https://app.codecov.io/gh/MatthiasValvekens/pyHanko/pull/314?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matthias+Valvekens#diff-cHloYW5rby9zaWduL2ZpZWxkcy5weQ==) | `99.37% <100.00%> (+<0.01%)` | :arrow_up: | | [pyhanko/sign/signers/pdf\_byterange.py](https://app.codecov.io/gh/MatthiasValvekens/pyHanko/pull/314?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matthias+Valvekens#diff-cHloYW5rby9zaWduL3NpZ25lcnMvcGRmX2J5dGVyYW5nZS5weQ==) | `100.00% <100.00%> (ø)` | | | [pyhanko/sign/signers/pdf\_signer.py](https://app.codecov.io/gh/MatthiasValvekens/pyHanko/pull/314?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Matthias+Valvekens#diff-cHloYW5rby9zaWduL3NpZ25lcnMvcGRmX3NpZ25lci5weQ==) | `99.84% <100.00%> (+<0.01%)` | :arrow_up: |

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[MatthiasValvekens]

Rebased & merged; thanks for your contribution!

[eduperottoni]

Thank you for your review and for all the job on pyHanko, @MatthiasValvekens!