- New PreferencesWindow gives us more space to add more
  features/configurations
- BlackBox now supports Freedesktop's style preference and allows for a
  light and a black theme to be set - implements #17
- New PreferencesWindow fixes #13
- WIP #43
- Removed linux and tango themes
- Added one-dark, pencil-dark, pencil-light, tomorrow, and
  tommorow-night themes
- Libadwaita bumped up to 1.2alpha