[sldev] SNOW-129 : saved accounts drop down menu

[Aleric Inglewood]

Requesting testers / reviewer for http://jira.secondlife.com/browse/SNOW-129

This patch causes logins/accounts to be remembered, also for different grids.
You can opt to have it remember the password too, so that logging in into any
of your accounts on any grid is just two clicks.

Originally written by Cypren and now with some extra chunk of code by me.