More work on emitter magic tools

Added heart & sparkle shapes.  Allowing for randomized rotation &/or
animation frames.  (Sparkles has frames, but does not rotate;
hearts & stars have no frames, but can rotate; hearts only +/- 45 degrees.)

For https://sourceforge.net/p/tuxpaint/feature-requests/266

docs/CHANGES.txt

@@ -11,8 +11,7 @@ https://tuxpaint.org/
     ----------------
     + WIP: Heart, Sparkle, and Star emitters
       Click and drag to leave a short trail of shapes.
-      - TODO: Hearts
-      - TODO: Sparkles
+      - TODO: Color support
       - TODO: Icons
       - TODO: Sound effects
       - TODO: Documentation