Allow to configure footer in Girder UI

[Xarthisius]

About, Contact and Report a bug are now configurable from wholetale plugin settings page.

[codecov[bot]]

Codecov Report

Patch coverage: 93.33% and no project coverage change.

Comparison is base (20e0406) 92.89% compared to head (e88019e) 92.90%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #577 +/- ## ======================================= Coverage 92.89% 92.90% ======================================= Files 61 61 Lines 4971 4986 +15 ======================================= + Hits 4618 4632 +14 - Misses 353 354 +1 ``` | [Impacted Files](https://codecov.io/gh/whole-tale/girder_wholetale/pull/577?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=whole-tale) | Coverage Δ | | |---|---|---| | [server/rest/wholetale.py](https://codecov.io/gh/whole-tale/girder_wholetale/pull/577?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=whole-tale#diff-c2VydmVyL3Jlc3Qvd2hvbGV0YWxlLnB5) | `91.30% <ø> (ø)` | | | [server/\_\_init\_\_.py](https://codecov.io/gh/whole-tale/girder_wholetale/pull/577?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=whole-tale#diff-c2VydmVyL19faW5pdF9fLnB5) | `91.64% <91.66%> (+<0.01%)` | :arrow_up: | | [server/constants.py](https://codecov.io/gh/whole-tale/girder_wholetale/pull/577?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=whole-tale#diff-c2VydmVyL2NvbnN0YW50cy5weQ==) | `91.37% <100.00%> (+0.47%)` | :arrow_up: |

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