Don't show context menu on finished multiselect.
Don't show context menu on finished multiselect.

Previously, we showed the context menu if a multiselect was finished
right away. Since we can select items individually now, it makes more
sense to just select the items as well and show the context menu later
via right mouse button or similar.

A multiselect can only add items to the selection, because that seems to
be easier to use. As before, shift+click can be used to deselect items.

The selection is cleared if the multiselect rectangle is empty and shift
is not pressed. This allows the user to click somewhere on the free area
to clear the selection again. If the shift key is pressed, it is not
cleared to prevent that a user triggers that by accident if he misses a
photo/album.

Zix17/Lychee,Zix17/Lychee,Zix17/Lychee