If welcome is enabled, use it to recover from a forgotten password (Closes hhucn/adhocracy.hhu_theme#243)
Improve password reset message when welcome_back is enabled
Merge branch 'develop' into welcome_back

Conflicts:
	src/adhocracy/lib/message.py
Merge remote-tracking branch 'liqd/develop' into welcome_back

Conflicts:
	src/adhocracy/controllers/user.py
	src/adhocracy/lib/auth/welcome.py
Fix syntax error
[welcome] Do not require password to be unset, and support the case of both welcome_code and reset_code
Merge pull request #336 from phihag/welcome_back

Welcome back users who forgot their passwords