Aa-srp

Fixed

- Capitalization for translatable strings

Changed

- Use `clean_setting` function from `allianceauth-app-utils` instead of reinventing the
wheel and have our own
- Translations updated
- Test suite updated

Fixed

- Exception: 'NoneType' object has no attribute 'character_name' when opening the
Dashboard view, and in one of the displayed SRP links is a fleet commander who
doesn't exist anymore.

Fixed

- Catch `AttributeError` exception on migration from the AA built-in SRP module
- Don't create SRP requests for non-existent users on migration from AA built-in SRP
module

Changed

- Spanish translation improved
- Korean translation improved

Changed

- Discord notification handling moved to its own module
- Message generation for the SRP Team message simplified
- Using `SITE_URL` from `local.py`

Changed

- Korean translation improved
- Spanish translation improved

Fixed

- Bootstrap CSS fix