MBS-357: Add a store for "remember me" tokens

This is for an implementation of http://fishbowl.pastiche.org/2004/01/19/persistent_login_cookie_best_practice/
MBS-357: Implement a new "remember me" system that doesn't involve passwords

Instead, we use random single-use tokens, in the approach proposed in http://fishbowl.pastiche.org/2004/01/19/persistent_login_cookie_best_practice/
MBS-357: Use generate_uuid_v4() to allocate remember me tokens

This is thought to be a little more cryptographically secure than
using our UUID generation in Perl, which currently uses a PRNG that
is not recommended for cryptography.
Merge branch 'mbs-358-remember-me'

* mbs-357-remember-me:
  MBS-357: Use generate_uuid_v4() to allocate remember me tokens
  MBS-357: Implement a new "remember me" system that doesn't involve passwords
  MBS-357: Add a store for "remember me" tokens

Conflicts:
	admin/sql/CreateConstraints.sql