HPCS-realm only landing page preferred to LBNL page that requires user choice from pulldown

[smasover]

Cf. https://github.com/ucberkeley/brc-draft-documentation/wiki/Logging%20into%20Savio#step-2-create-a-pledge-profile

Step 3 (choose the realm) is one more place a user might make an innocent error. Would it be possible (I think it would be preferable) for BRC HPC (Savio) users to be directed to a "Pledge Enrollment" page -- other than LBNL's, here -- that does not require user-selection from a pulldown (if a pulldown is presented HPCS should be the default value).

[aronr]

This also has the merit of making it possible to present a UCB- and/or Savio-themed Pledge Enrollment page. (Any themed page must still give prominent credit to LBL.)