Add functions to alter sprite bitmaps on the fly

[comradeshook]

• Added Lua-accessible bitmap manipulation functions to MOSprites:

   GetSpritePixelIndex(int x, int y, int whichFrame) - Returns the color index of the pixel at the given coordinate on the given frame of the sprite ((0, 0) is the upper left corner!)
  
   SetSpritePixelIndex(int x, int y, int whichFrame, int colorIndex, int ignoreIndex, bool invert) - Sets the color of the pixel at the given coordinate on the given frame of the sprite, skipping if the pixel has same color index as given in "ignoreIndex". If "invert" is set to true, only pixels of that color index are set.
  
   GetAllSpritePixelPositions(const Vector& origin, float angle, bool hflipped, int whichFrame, int ignoreIndex, bool invert, bool includeChildren) - Returns a list of vectors pointing to the absolute positions of all pixels in the given frame of the sprite, rotated to match "angle", flipped to match "hflipped" and positioned around "origin", providing a full silhouette of the MOSprite. "IgnoreIndex" and "invert" are like above, "includeChildren" denotes whether or not to include all children of the MOSprite (no effect if not at least an MOSRotating).
  
   GetAllVisibleSpritePixelPositions(bool includeChildren) - Simplified version of the above, returning a list of absolute positions of the visible pixels of the current frame of the sprite as it is currently drawn.
  
   SetAllSpritePixelIndexes(int whichFrame, int colorIndex, int ignoreIndex, bool invert) - Sets all pixels in the given frame of the sprite to the given color index, ignoring and inverting as above.
  
   SetAllVisibleSpritePixelIndexes(int colorIndex) - Simplified version of the above, sets all visible pixels of the currently visible sprite to the given color index.
  

• Added Material Lua function GetColorIndex(), which returns the color index of the calling material.

• Fixed MOSprite:UnRotateOffset() giving the wrong results on HFLipped sprites.

Allows modification of MOSprite bitmaps on the fly, which can give neat effects like discolouring and deformation. Surprisingly, doing this DOES modify how MOSR's get hit without any further modifications.

[Causeless]

Looks great!