Fixed a bug that lost login information between full page refreshes

The authentication code uses the players collection to find the logged in player. The players collection is loaded asynchronously on each page load. It seems that almost always the authentication code was trying to query the players collection before the data had been loaded into the players collection, so it always appeared to be empty. And then the authentication code would so "oh, no player logged in apparently"
Converted the "invite by facebook" and "invite by email" screens to modals
Updated the "invite friends by facebook" dialog

It displays friends grouped by the first letter of their name and scrolls the overflow.
Only display those facebook friends you can actually invite

Only shows facebook friends who have logged into Doodle Monster.