Add Users and Sessions

Squashed commit of the following:

commit 1c032da10ad84c76c2ec8489c811d96a4278215a
Author: dianaliu <diana.g.liu@gmail.com>
Date:   Sat Feb 15 19:54:47 2014 -0500

    Add and update User and Session tests

commit 6b254f62e5b4c5f0b29c43a18cca9ed6f79e304e
Author: dianaliu <diana.g.liu@gmail.com>
Date:   Sat Feb 15 19:25:50 2014 -0500

    Add top nav, sign up and sign in. Style forms

commit cb39b370e5d6a121c6ae545baf40c26cba1965bb
Author: dianaliu <diana.g.liu@gmail.com>
Date:   Sat Feb 15 18:41:47 2014 -0500

    Update login view

commit bc2282a9557ac2ea08655ddb68f1daefa133b5e0
Author: dianaliu <diana.g.liu@gmail.com>
Date:   Sat Feb 15 18:25:13 2014 -0500

    Auto login user after sign up

commit 383e475196f2300cdb799de3953ab9cf8fbb5b85
Author: dianaliu <diana.g.liu@gmail.com>
Date:   Sat Feb 15 18:15:53 2014 -0500

    Update wording for signup errors

commit 74660f48af7503c2e535381ba300e0921b62eb96
Author: dianaliu <diana.g.liu@gmail.com>
Date:   Sat Feb 15 18:08:23 2014 -0500

    Update gems

commit e097b3636afaa0f2c0a4cb8d67e87383fb3345df
Author: dianaliu <diana.g.liu@gmail.com>
Date:   Fri Feb 14 16:55:27 2014 -0500

    Begin adding sessions

commit 64b84d715aadfb28e1b7163101073698a5293178
Author: dianaliu <diana.g.liu@gmail.com>
Date:   Wed Feb 5 01:12:37 2014 -0500

    Style form a lil

commit 184c3066c7f742a623d13123bb21ea916f7dd575
Author: dianaliu <diana.g.liu@gmail.com>
Date:   Wed Feb 5 00:46:10 2014 -0500

    Add UserMailer to confirm registration

commit 2f3f51e97c93dcd4cc22a315f0f413d8ae1e51cc
Author: dianaliu <diana.g.liu@gmail.com>
Date:   Wed Feb 5 00:08:49 2014 -0500

    Add users_controller_spec

commit 79e9ff5e63476bc5f962699fa8d2d1b11cac3d1f
Author: dianaliu <diana.g.liu@gmail.com>
Date:   Tue Feb 4 23:00:45 2014 -0500

    Simple User#create form on index with client-side validation

commit 1bbd971da1cd5f40020251d0b67f30075f1fb688
Author: dianaliu <diana.g.liu@gmail.com>
Date:   Tue Feb 4 21:38:38 2014 -0500

    Create User and EventsUsers relationship