CommonLibrary had some undesired knowledge of UI. Split AppPreference
and UIPreference. Then move some more stuff from AppUI* to UILibrary.
WARNING: this forgets existing UI preferences (e.g. favorite servers).
- Move about subviews to UILibrary
- Refactor about to single coordinator + platform views
- Refactor debug log to single view + content views
- Take out debug log routes from about routes
- Rename Settings* to Preferences*
- Reuse empty modifier in debug log
- Fix a visual bug in .themeTrailingValue() (extra Spacer)
Preparation for #914