next round of updates
- remove tab bar
replacement: switch-to-xxx-tab actions in the view menu
you should not often need to manually switch the tab (except maybe playlist) --> let the application behave in a more intelligent way

- remove xmlgui stuff
KShortcutsDialog takes care of custom key bindings

- nicer fullscreen mode
we turn the main window into fullscreen instead of showing a secondary window
this is possible now because we have more control over the gui components

- various cleanups