Custom favicon and title

[WithoutPants]

Adds support for custom favicon by reading from favicon.ico from the config directory. Uses the custom favicon if it is present at startup.

Adds Custom Title setting to the interface settings. Replaces Stash with whatever is in the custom title. Defaults to Stash if empty.

Resolves #5072

[discourse-stashapp]

This pull request has been mentioned on Stash. There might be relevant details there:

https://discourse.stashapp.cc/t/rebrand/1603/5