2.5: Added basic insert/remove keyframes from UI buttons.

- I key over a button inserts a keyframe.
- Alt+I removes a keyframe.
- With right mouse button a menu with these options pops up.
- Buttons are colored green if the property is animated, yellow
  if it is on a keyframe. I followed the colors from the UI
  mockups, but the flicker on keyframes seems too distracting in
  practice?

- This only works for properties on the ID itself at the moment,
  path callbacks need to be filled in for all structs but mesh
  still.
- It doesn't work when you're over a related label, that needs to
  be made to work.
- I made it insert keyframes outside of any keyingset. Not sure
  how this is supposed to integrate?

source/blender/editors/animation/anim_ops.c

@@ -382,6 +382,8 @@ void ED_operatortypes_anim(void)
 	WM_operatortype_append(ANIM_OT_delete_keyframe);
 	WM_operatortype_append(ANIM_OT_insert_keyframe_menu);
 	//WM_operatortype_append(ANIM_OT_delete_keyframe_menu);
+	WM_operatortype_append(ANIM_OT_insert_keyframe_button);
+	WM_operatortype_append(ANIM_OT_delete_keyframe_button);
 	WM_operatortype_append(ANIM_OT_delete_keyframe_old); // xxx remove?
 	
 	WM_operatortype_append(ANIM_OT_keyingset_add_new);