Adds theming to FluentHub. This can be achieved by creating multiple files with different Primer resources that the user can select.
Motivation & Context
Related: #158
Related: #163
### Tasks
- [ ] Improve border and some of SolidColorBrushes which contains in FluentHubDefault.xaml theme resources to use system default theme resources.
- [ ] Add theme switching helper class methods
- [ ] Add various GitHub's official themes
- [ ] Display those themes in app appearance settings page
Description and Motivation
Adds theming to FluentHub. This can be achieved by creating multiple files with different Primer resources that the user can select.
Motivation & Context
Related: #158 Related: #163