Started the implementation of shibboleth in mweb2, refs #376

Very first changes, migrating a bit of what was done in the master branch.
Not only copying the code, but improving it as much as possible.
Still a lot to be done, but already included tests for most of what was done
so far.

Had to add the migrations as done in master (using the same timestamps) so
the migration from the current master to branch-v2 will work (refs #987).
Implement a big part of associating a user with a shib account, refs #376

Not entirelly done yet, but the login, creation of ShibToken's, and creation
of a new user account are well under way, mostly finished.
Finish the basics of ShibbolethController and its views, refs #376

There's still a few TODOs in the code, but what is implemented in the master
branch was already migrated, the rest is improvement.
The views are working but some still need to be reviewed. There are references
to shibboleth throughout the application that need to be reviewed.
Version functional version of login via shib done, refs #376

Finished the last things that had to be done, specially in the views. There
are still TODOs in the code, but the login via shibboleth is already working.
These TODOs are improvements that can be done in the future.
Merge branch 'issue376' into branch-v2
More adjustments in news and join requests

Added tests and reviewed abilities, specially.
There's still things to be improved and a lot of tests to be added. Included
a few TODOs for some of these things.

refs #790