Update 1.5.1 and release 2.0dev

Hello,

a last update for privacyidea 1.5 was published.
The version 1.5.1 contains a minor fix to handle users, that contain an
@-sign.
So a user like user@example.com@realm1 can login at selfservice and
authenticate.

At the same time, i merged the github branch version 2 to the master branch.


Finally, we get a green code coverage sign :wink:

The version 2.0 is still a development version. But you are welcome to
check it out!
The database structure was recreated and the backend was rewritten with
flask.
The Web UI has a more modern look, that works well on mobile devices.

Any feedback is highly appreciated.

Kind regards
Cornelius