Implemented Files app (#33)

- Created Files app to browse PC and ESP32 files.
- Refactored toolbars so it's now a proper widget and allows for changing its properties from the app
- Toolbar now has extra action buttons
- Settings app now has a proper icon
- Minor cleanup in Desktop app

docs/ideas.md

@@ -12,6 +12,10 @@
 - Support for displays with different DPI. Consider the layer-based system like on Android.
 - Display orientation support for Display app
 - If present, use LED to show boot status
+- 2 wire speaker support
+- tt_app_start() and similar functions as proxies for Loader app start/stop/etc.
+- tt_app_set_result() for apps that need to return data to other apps (e.g. file selection)
+- Make a statusbar service that apps can register icons to. Gui can observe its status changes?
 
 # App Improvement Ideas
 - Sort desktop apps by name.