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.
Try to sort all GIMP_ICON_* defines into FDO categories like in
https://specifications.freedesktop.org/icon-naming-spec/latest/ar01s04.html
Add defines for all icons we override, rename some icons to their FDO
standard names, and mark the ones we duplicate with a comment so we
don't forget to rename those to standard names in 3.0.
Nobody has them anymore, and they are deprecated in GTK+ 3.x. This
also fixes all conflicting mnemonics except those I missed, but we can
fix them now.
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.
Introduce item-options-dialog.[ch] which abstracts this away and use
it from the layer, channel, vectors options dialogs. This is all
pretty ugly but better than duplicating that code three times. The
vector-options-dialog is now completely pointless but I kept it anyway
for now, let's see what unique path options we come up with.
