Implement double buffering

[jens-maus]

@tboeckel created the issue:

Phenomenon

Certain classes (i.e. Title.mui) must be redrawn completely for any change to be applied (i.e. changing the active tab). This might cause a graphical overhead which can be be seen more or less obviously, depending on how fast the redraw can be done on a specific hardware.

Background analysis

Drawing such complex objects to an off-screen bitmap first and then blit this bitmap into the visible part of the window will eliminate the flicker effect. However, all classes must be able to handle the possibly shifted coordinate system to render themself at the correct position.

Implementation recommendation

If certain classes cannot be enhanced to respect the shifted coordinate system it may be necessary to introduce a black list of faulty classes which need to be drawn directly instead of to the off-screen bitmap first.