Adds a Settings tab to the UI. I currently added the skeleton UI, and also a basic SettingsViewModel.
I set this MR to WIP because the SettingsViewModel might need to be instantiated a little differently than the other UI viewModels, because it needs to be used in the top level BriarUI file, as well as the SettingScreen file and I wasnt sure the best way to implement this.
Also it still needs to add proper database reading and writing to save and load settings between sessions.
Closes #94 (closed)