oauth2server: confidential and public clients

* Adds option to new application form to ask user for client type. (addresses #2113)

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
77: D102 Docstring missing
84: D102 Docstring missing
92: D102 Docstring missing
111: D101 Docstring missing
127: D101 Docstring missing
148: D101 Docstring missing