This adds a widget called `CcKeyboardShortcutRow`, sub-classing
`GtkListBoxRow`, to handle a shortcut row. This makes the implementation
a bit tidier, rather than handling it all in `CcKeyboardPanel`, and
allows the widgets that compose the row to be laid out in xml.
This is a prerequisite for moving the shortcuts to a new dialog.
This commit includes all the changes that seem to be necessary for
CcKeyboardItem to be used for dealing with multiple keybindings, without
(yet) changing the user interface to expose this.
The `primary_combo` and `binding` fields of `CcKeyboardItem` are
removed, in favor of the existing `key_combos`. No combination is
"primary", since all of them can now be seen and changed equally.
We treat `CcKeyboardItem.key_combos` as a set, that a combo can be added
to or removed from. Though it continues to be represented as a `GList`,
instead of a `GHashTable`, to preserve ordering.
A lot of the keyboard panel code relied on the assumption that only one
combo can be set for each setting, so this required a variety of
miscellaneous changes.
We don't need to track them much specifically, as we delegate pad
button mapping UI on GNOME Shell. It is however possible to have
tablets with 0 to N pads (upper bound within sanity = 2), so we
must at least reflect that in the "Map Buttons..." button visibility.
This distinction is most important for the combination of EKR plus
Cintiq 27QHD, as this is a pad-less tablet, for which we wouldn't
usually show the "Map buttons..." action.
https://gitlab.gnome.org/GNOME/gnome-control-center/issues/415
This puts stylus/pad tracking on 2 separate levels. The CcWacomPanel
will look for styli, and treat them as "device leaders", adding a
CcWacomPage for them.
The CcWacomPage will then track the related pad, and update the
"Map buttons..." action visibility according to it.
This simplifies tablet page creation (eg. have it completed in one
step), and decouples the device grouping logic from CcWacomPanel,
which will be useful in future commits.
