Allows to use ctrl+d to close tabs from the buffer completion widget
when they are selected. Respects current tab settings like whether you
can close the last tab in a window.
Had to change the `rebuild()` method to use `setData()` when possible
because the selection was being lost if the whole model was being rebuilt.
Current problems are:
1) When opening a new window while you already the tab completion open on
one window a category is added for the new window but new rows in
that category aren't picked up. Interesting if you open a third
window then close the second window the completion display is now
correct... I can see that the model is being updated correctly but I
am not sure why that isn't propagating to the view. Not sure whether
it is worth looking into (further) either.
2) Bit of duplication of code, it iterates over the window registry
twice. Could put everything in one loop but then that would be
dependant on the current behaviour of the `tab_closed` signal being
called with the relevant `tabbed_browser` still existing but with the
`shutting_down` flag set.
3) I'm still using just the one `rebuild()` method and removing items from
the end then calling `setData` on everything rather than having special
`on_tab/window_closed` methods (or partial functions) that delete the
actual corresponding item. Because if I did that I would also have to
special case tab moves etc.
32edd35c7a