so the sidebar is listening to the old controller which has been disposed[1] so
when print preview exits and yet another controller replaces the print preview
one then the sidebar still doesn't listen to the current one.

framework broadcasts COMPONENT_DETACHING/COMPONENT_REATTACHED around these
changes, so if we listen to them we can keep attached to whatever is the
current component

[1] note that ContextChangeEventMultipler doesn't inform clients that the
controller has been disposed, this remains unchanged here

Change-Id: I141509d4a262307afd7dcfc3d77de6cdd6dbfa5f
Reviewed-on: https://gerrit.libreoffice.org/33758Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>