Randomise angles of rotation for snapshots in a stack

[snwau]

Optionally randomise angles of rotation (i.e. positions) of all snapshots below the top most snapshot.
Configurable via a property, OFF by default.

Randomisation should occur on change of image property and change of display mode via displayAsStack property.

Randomisation is restricted by:

• Between a predefined Minimum & Maximum allowable angle of rotation
• Consecutive snapshots should be seperated by a minimum angle to avoid equal angles of rotation overlapping snapshots.