ShipsShaders updates

Numerous updates:

BackgroundLearner and MotionCursor parameters revised to a state that
gets great results.

BackgroundLearner buffers now maintain aspect ratio identical to program
window for better user correspondence.

Light can now be set to Directional mode, which illuminates the entire
screen from the same vector.

RenderManager has background field, and compositor shader incorporates
this into field.

RenderManager sets a default warp state, and warp shader now correctly
renormalises values.

Warp shader now automatically performs chromatic aberration.

Ship has numerous changes, including a coloured explosion and a cloaking
device. The cloak activates on ships with the cloakOnInactive flag true,
when they have not fired any shots or used navigation systems in a short
period. Slave ship entities such as turrets also comply.

ShipManager no longer returns exploding enemies as targets.

Removed graphics rendering from Story. It retains the ability to save
image sequences.