Progress, track duration, and seek support

[jpochyla]

Playback progress, together with total duration, would be probably the last things we miss.

[Sinono3]

Progress:

• [X] Linux:
  • [X] Progress
  • [X] Track duration
  • [X] Seek
• [x] Mac
  • [X] Progress
  • [X] Track duration
  • [x] Seek
• [X] Windows
  • [X] Progress
  • [X] Track duration
  • [X] Seek