autocomplete: use select2 when selecting users or groups to give permissions This is a minimal change to MembersAutoComplete, inspired by Dominik Ruf. The UX is slightly different than before, with select2 putting up an extra input field, already before typing anything. We use minimumInputLength 1 to get the same behaviour as before and avoid displaying all users in a list.

# requirements.txt file for use as "pip install -r requirements.txt" as a
# readthedocs compatible alternative to "pip install -e ." which is a working
# alternative to "setup.py develop" which doesn't work with Mercurial 3.7
.