Add gimp_item_get_merged_color_tag(), which returns the color tag
of the nearest ancestor (including the current item) that has a
color tag other than NONE. Use this function in GimpItemTreeView,
instead of gimp_item_get_color_tag(), to set the cell color of
items, so that item's with a NONE color tag inherit the color of
their parent. Add a boolean "inherited" parameter to
gimp_get_color_tag_color(), which indicates if the color tag is the
item's actual color tag, or an inherited color tag, and modify the
returned color accordingly, so that inherited colors are less
saturated/lighter than non-inherited ones.
Add property "color-tag" of type enum GimpColorTag to GimpItem so all
layers, channels and paths can be tagged with a color.
For interoperability, use the color list from Krita which is a
superset of Photoshop's colors.
Features a "Color Tag" submenu in the layers, channels and paths
menus, a row of color radio buttons in the properties dialogs,
undo and PDB API.
As a side effect, some common code is now factores out into
items-actions.[ch] and items-commands.[ch] which adds visible, linked
and lock actions for layers and channels.
Michael Natterer