phab - configurable login message by auth type

depending on the type of login a phabricator instance
allows to be used for auth (SUL account, LDAP account,
both, maybe others in the future..), change which
template is being used for the HTML of the login screen

and change the links to proto-relative URLs as pointed
out by greg-g, except that https://phabricator.org
doesn't work. connecting...

Change-Id: Iae4ab606563579973ad3731d0ebcf39d665634f9
Merge "phab - configurable login message by auth type" into production