Remove test_pyflakes.
Fix SYWEB-109 : No error if HS rejects the username in registration.

Display all error messages from the server when registering, rather
than just the types of errors the client recognises.
HandleRoomMember: handle correctly prev_content
Implement SYWEB-121 : Display JSON when clicking messages.

JSON is displayed as a modal dialog via AngularJS' bootstrap module,
"ui.bootstrap".
SYWEB-121: Have some bootstrap files.
Don't clobber existing css
Fix SYWEB-114 : Error message when trying to invite a user already in the room.
Remove duplicate join_event from create_room
Merge branch 'develop' into event_signing