+ Fixed some convolution matrices.
+ Fixed editors_draw_sprite_tiled & control_tool for tiled mode in
transparent layers (non-Background).
+ Added gfxobj_id.
- Removed referenced stock (replaced with the ImageRef structure).
+ Fixed the whole 'target' stuff between effects and target_button.
+ Fixed app_get_fg_color & app_get_bg_color to return the black color
instead of mask when a `Background' layer is actived.
+ Added get_color_for_layer & fixup_color_for_layer.