Fix Bug 770 and 771

Bug 770:

X11Window.c:
  - Request focus _before_ enabling EWMH flags (fullscreen or above) after resize
    and temporary invisibility.
    This actually allows us to keep the focus after resize and repositioning!

  - Set _NET_WM_BYPASS_COMPOSITOR implicit analog to _NET_WM_STATE_FLAG_ABOVE

  - Clean up _NET_WM_* flag names, avoiding name space collisions, i.e. adding FLAG!
  - Remove dead _NET_WM_STATE setting via direct window property (not working anyways)
  - Remove dead code: FS_GRAB_KEYBOARD

X11/WindowDriver.java:
  - Enable _NET_WM_STATE_FLAG_ABOVE temporarily if
    FLAG_IS_FULLSCREEN && !FLAG_IS_ALWAYSONTOP

  - Override focusChanged(..) to react on focus lost/gained
    in case of temporarily enabled _NET_WM_STATE_FLAG_ABOVE.
    If focus is lost, disable _NET_WM_STATE_FLAG_ABOVE,
    otherwise re-enable it.

WindowImpl.java:
  - FullscreenAction.run: Always use 'FLAG_IS_FULLSCREEN_SPAN'

+++

Bug 771:

WindowImpl.java:

  - Keep fullscreenMonitors and fullscreenUseMainMonitor values intact,
    allowing them to be tracked. Remove duplicates in FullscreenAction class.

  - MonitorModeListenerImpl.monitorModeChanged:
    Add fullscreen path: If the changed monitor is part of fullscreenMonitors,
    recalculate the viewport union and reset position and fullscreen-size.

  - MonitorModeListenerImpl: Try to regain focus after successful mode change.