BitmapCache Improvements

[Stefan4472]

• BitmapCache shouldn't be static
• Should take array of BitmapID's to load on initialization (which it then loads) as well as a scaling factor to scale each image to
• The bitmaps are actually stored with String-Bitmap pairs. When a bitmap is added using a BitmapID object, it is stored under the BitmapID's toString() method.
• Has a put(String key, Bitmap bmp) to put specified bitmap under the given key
• Two getters: one uses a BitmapID (which is converted into the String key) and the other uses a simple String