This patch adds an on_context_menu_request hook to GAbstractView which is
currently only invoked by GTableView. We also pass along the entire context
menu event, so that anyone using the hook can use it for menu placement etc.
Implemented this by letting GAbstractViews provide a GModelEditingDelegate
for a given index, which then knows how to create and setup a custom widget
appropriate for the data type being edited.
Also run it across the whole tree to get everything using the One True Style.
We don't yet run this in an automated fashion as it's a little slow, but
there is a snippet to do so in makeall.sh.
Now you can hook activation via GAbstractView::on_activation.
The design still isn't quite right, we should eventually move the selection
away from the model somehow.
GAbstractView should be able to manage the high-level editing logic, as long
as subclasses implement content_rect(GModelIndex) so we know where to put
the editing widgets. :^)
This is pretty shaky still, but the basic idea is that you subclass GModel
and return true for editable indices. The table view also needs to have its
editable flag set.
