Add support for dynamic footer links

[MythicManiac]

Implement a simple system for adding extra footer links via a DB model which get rendered in addition to the pre-existing static footer links.

Examples of the CSS behavior on different screen sizes:

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (463a1ea) 92.93% compared to head (5c9f9f9) 92.95%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1015 +/- ## ========================================== + Coverage 92.93% 92.95% +0.02% ========================================== Files 314 314 Lines 9042 9070 +28 Branches 804 806 +2 ========================================== + Hits 8403 8431 +28 Misses 530 530 Partials 109 109 ```

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