migrate old user/group autocomplete code to use data-complete* attributes instead

one thing to note: old autocomplete code took inputs with name matching
/WatcherAddressEmail[123]/ as multiple email addresses(they are used in
/Ticket/ModifyPeope.html), but they are not actually(yet), so I chose to not
make the change accordingly, i.e. I just took them as single ones.
Rename userautocomplete.js now that it's used for groups too
Merge branch '4.2/refactor-user-group-autocomplete'