Login page does not remember the last realm used by user

[TheWitness]

Describe the bug
When you login using one of the LDAP options, Cacti does not remember the last login realm. So, you end up having to change it every time.

To Reproduce
Steps to reproduce the behavior:

1. Setup LDAP authentication
2. Login and note that LDAP is the default
3. Login as the 'Local' admin then logout
4. Note that the default Realm is still LDAP

Expected behavior
Cacti should remember the last login realm for a browser.