Config changes to enable MongoDB with Ion Auth

Default Mongo database name is "mongo" for now, but we
could easily change that to whatever we want: sfweb, maybe.
Autoload the Ion Auth library
Use a (randomly-generated) session encryption key
Use bcrypt instead of SHA1 - much more secure

Note that the Mongo database will need to be updated to
set the admin password to the bcrypt hash for "password";
the syntax for doing this (assuming you've already loaded
the starter data that Ion Auth provides) is as follows:

db.users.update({'email': 'admin@admin.com'}, {'$set': {'password': '$2a$07$SeBknntpZror9uyftVopmu61qg0ms8Qv1yV6FG.kQOSM.9QhmTo36'}})
Make Login button on front page functional

Note that the "Create an account" (registration) link is not yet
functional, so the Login button isn't as useful as it could be.
Fix a few Ion Auth-Mongo bugs

Most of these bugs are caused by mild mismatches between
how Mongo returns rows and how an SQL database returns
rows: the SQL database apparently returns them as a hash
table (a dict in Python terms), whereas the Mongo connector
appears to be returning rows as arrays (lists in Python terms).

I'll eventually want to submit this to the Ion Auth issue
tracker on GitHub.