[N/A] Improve app's backend

[therealbluepandabear]

App is pretty stable but not good enough, here are some things to improve:

• [ ] Improve color palette stability: the backend code is poorly designed
• [ ] #159
• [ ] Improve adapter code for brushes
• [x] Add tests which are actually useful that can be run before each release
• [ ] Improve backend code for shape tools
• [x] Improve frontend XML code by utilizing custom views for the primary and secondary color
• [x] Stabilize 'Save in Background' by improving backend logic