Add a simple GUI to be used in the interactive anti-drift

This simple GUI shows the XY, XZ and ZY projections of two stacks
as magenta/green overlay.

Cursor up/down/left/right and PageUp/PageDown control the
three-dimensional shift.

Hitting the Return key will call a single callback function and close
the GUI.

The main() method demonstrates how this class should be used. It runs in
the Fiji Script Editor and expects the Fly Brain to be loaded from
File>Open Samples and then split via Image>Color>Split Channels...

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>