Patch: adjust grouping behaviour

[Simon Frei]

Currently when a grouped image is selected all operations (tagging,
renaming, ...) are only applied to the head of the group. This is not
consistent with the options to display items: In iconview, there is
grouped and ungrouped, in tableview ungrouped, grouped and tree. So I
have control over whether I want to display images individually or as
groups. However this control does not extend to actions.

The attached patches change the behaviour:
When images are grouped or not expanded in treeview, actions apply to
the selected images and the grouped images. In Ungrouped view or when
images are expanded in treeview, actions apply only to the selected images.

In the process I uncovered some more or less related issues, that is why
I have split the patch up. Every single one is functional.
"allchanges.diff" is, as it name suggests, the combination of all the
other patches.

grouping.diff
This is the main change that alters the behaviour as described above.

connect.diff
Currently there is no tracking of whether items are expanded or not in
treeview. This results in erratic behaviour, e.g. tagging applies to
different images depending on cursor moves before. This connects the
treeview expanded and collapsed signals to the signal, that signifies
that anything has changed.

rename.diff
Currently the interactive rename function is executed in the iconview
context in any case. Now it is executed in the currently active view for
correct selection.

next.diff
Little correction where a change was always applied to iconview, now it
is correctly applied to whichever view is currently active.

All the changes are also available on https://github.com/imsodin/digiKam
if that is more convenient. This is related to bug 294578.

Cheers,
Simon
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