Support for Raspberry Pi

[bdlukaa]

Add support for Embedded Environments.

• Video rendering support (linux(pi): implement unity_video_player_flutter #194)
  Video is the core part of the application. We must ensure the video rendering software is stable enough to release it.
• Adapt the app for embedded devices (feat: Embedded platforms support #199)
  Some functionalities are not available in an embedded environment, or have to be written from scratch.
• Adapt the user interface
  The embedded user interface should be similar to the tablet's.
  • All panels and sidebars compacted by default
  • Left navigation should be used over top navigation

Additional context

• https://github.com/ardera/flutter-pi