delta-find: move the emotion of parents in a dedicated method
After splitting the filtering, and with the `_candidate_groups` layer removed,
we can start splitting the group generation too. This helps to organize this
code and make it easier to modifying the future.
#require docutils gettext
$ $TESTDIR/check-gendoc de
checking for parse errors
Die Dateien werden dem Projektarchiv beim n\xc3\xa4chsten \xc3\x9cbernehmen (commit) hinzugef\xc3\xbcgt. Um dies vorher r\xc3\xbcckg\xc3\xa4ngig zu machen, siehe:hg:`forget`. (esc)
warning: please have a space before :hg: