uhm, hai

i fixed the gcc -fpermissive complains in IGraphicsWin and added a function to IGraphics, FindBitmap(), and also added an argument to RetainBitmap() ... in order to make an alternative function for loading the png files from disk and adding them to the s_bitmapCache

one of the fixes required removing a "const" somewhere related to some tooltips or something, no idea if it's okay