Use common progress bar

[Mathias Brodala]

A custom progress bar should be written which takes care of all required updating as well as seeking.
Custom drawing could be used to add visual markers (useful for bookmarks plugin, an A-B-Repeat and possibly cue sheets).
Buffering progress or similar could also be hinted at by custom drawing.

[reacocard (reacocard)]

I like the idea of a marker API, though figuring out how to make it follow the GTK theme will be interesting. Each marker could have callbacks when its clicked, and setting markers could be done with a right-click ProviderMenu on the bar.

Buffering I'm not so sure of as gst doesn't provide us a lot of info in this regard, but we could at least move the buffering message into the progressbar text itself.

Another idea - automatically adjust update frequency based on size of the bar and length of the track, so it moves perfectly smoothly. May need some work to make this not be cpu-hungry.

[Mathias Brodala (mathbr)]

Fixed with r3599. Markers can be added via the new progress bar context menu and by default offer to jump to them, move them and remove them. Both menus are extensible through providers.