MainWindow: implement gestures

Allows gestures in the CrossSectionWidget (TRAC #2655).  This works
because the CrossSectionWindow is "disabled", and therefore
mouse/touch events are delivered to MainWindow.
MainWindow: fix mouse event regression

The previous commit broke mouse event delivery to child windows.
D'oh!
Merge branch 'v6.5.x'
Replay: fast-forward

This is the first sketch of a fast-forward button.  It accelerates the
Replay Timer.  This doesn't work too well yet, because the MergeThread
and CalculationThread are asynchronous and throttled.  UI feedback is
missing, too.
Android/Main: update TRAC URL
Android/Bluetooth: join the connect thread in close()

Fixes a race condition leading to a crash (TRAC #2636, #2656): when
the port is being closed just when BluetoothClientPort is in the
middle of socket.connect() and setPort(), a new InputThread gets
created that is orphaned instantly, nobody is aware it exists (and
refers to the NativeInputListener).  After close() returns, the native
code deletes the NativeInputListener.  When the orphan InputThread
invokes the NativeInputListener, XCSoar crashes.

The solutionb is to wait until BluetoothClientPort's thread finishes
before cleaning up the ProxyAndroidPort.  This ensures that no such
orphan objects exist.
Android/BluetoothServerPort: remove obsolete method isValid()

Superseded by MultiPort.getState().
Android/BluetoothServerPort: add missing "@Override" annotations
Android/BluetoothServerPort: remove obsolete method setListener()

Fixes input on the Bluetooth server by not overriding
MultiPort.setListener().
Android/BluetoothServerPort: move code to closeServerSocket()

Safely clear the serverSocket property.  close() and
closeServerSocket() both do not need to be "synchronized".
Android/BluetoothServerPort: fix deadlock in run()

Call closeServerSocket() instead of close().  The latter joins the
thread which we're currently running.  Fixes regression by 6405ca.
Android/BluetoothServerPort: implement getState()

Catch serverSocket==null.
release v6.5.1
NEWS.txt: move misplaced 6.6 line
Merge tag 'v6.5.1'
NEWS.txt: prepare version 6.5.2
po: update Polish translation
po: update Finnish translation
AbstractTaskFactory: more API documentation
Dialogs/TaskPropertiesPanel: hidde FAI finish height if not a FAI task