HaikuDepot: Switched back to actual BTabView

 * Instead of showing all package actions along the bottom
   of the window, only the applicable actions are shown, but
   besides the package title.
 * The radio buttons are gone, instead an actual BTabView is
   used, but now in a more pretty way.
 * The package info content stretches to the window border
   which will make showing a vertical scroll bar look better.