Bilbao access is back

[briantoby]

Access to the Bilbao website from inside GSAS-II is now possible again. It requires an extra set of steps, to register with the BCS site and save the token provided into GSAS-II. How to do this is documented in a new tutorial. A few people have tried this and there have been no complaints.

There are a few things that are still needed:

• The registration tutorial needs to be added to the tutorial index
• The existing tutorials that discuss access to Bilbao need an update to reference the registration tutorial
• Supergroup generation is not fully implemented for monoclinic and triclinic systems
• A new tutorial on subgroup and supergroup generation needs to be completed

(closing #294)