Groups

Groups appear to be okay.  Diners now have a current group id, can join groups, can create groups w/ password, and can switch groups.

~~TODO: basically every ingredient/meal/(payment?) and associated queries need to have a group id associated with them by abusing the current group id.~~

~~TODO: Help user get to groups page if they are not in a group.  (redirects? help message? #dealwithit?)~~

These are done now.