Fixed issue with adding roles (bigbluebutton#1051)

allow for mail system without authentication (bigbluebutton#1019)

* allow for mail system without authentication

* try to fix travis build

Translate /config/locales/en.yml in zh_CN (bigbluebutton#980)

translation completed for the source file '/config/locales/en.yml'
on the 'zh_CN' language.

Co-authored-by: Jesus Federico <[email protected]>

Merge pull request bigbluebutton#971 from bigbluebutton/v2.5-alpha

Release v2.5

Release: Major 2, Minor 4, Revision 2

Release: Major 2, Minor 4, Revision 2, Release Candidate 1

Stable Release: Major 2, Minor 4, Revision 1

Stable Release: Major 2, Minor 4, Revision -

Release Candidate: Major 2, Minor 4, Revision -, Tag rc1

Beta Release: Major 2, Minor 4, Revision -, Tag b3