MediaPlayer: Move winding code into its own function.
MediaPlayer: Add Duration, Position and Seek properties.

These allow getting the duration of the currently playing item and the
current playing position as well as setting the absolute position and
seeking by relative time via scripting.
HaikuDepot: Better feedback while installing

 * Replace the package action button with a download-progress bar
   while the package downloads. Needs some tweaks to the layout code
   to avoid pushing the rest of the title area to the left, but its a
   first step. An additional dedicated area somewhere in the UI which
   lists all on-going tasks would be nice as well.
Added HAIKU square graphic.

This is used on the github page and several other places that support gravatar.