Store gravatar in database. Closes #42

Squashed commit of the following:

commit 13fca0397a746cb5466ecb46ea79dc494837a7fb
Author: Catherine O'Neill <cathzozo@gmail.com>
Date:   Fri Sep 12 17:05:11 2014 -0500

    all passing

commit 8138dcdccc31d9696de4d827f2606ee8a0637369
Author: Catherine O'Neill <cathzozo@gmail.com>
Date:   Fri Sep 12 17:04:17 2014 -0500

    vcr added, 1 test still failing

commit def516c9383a526d5c4762b9f2aa3eb01606958c
Author: Catherine O'Neill <cathzozo@gmail.com>
Date:   Fri Sep 12 16:55:56 2014 -0500

    refactored repeated lines into before block

commit fb6277a01756c977db392ebc9136df97d639d9d6
Author: Catherine O'Neill <cathzozo@gmail.com>
Date:   Fri Sep 12 16:54:54 2014 -0500

    getting user info in SessionsController#create instead of name in User#create_with_omniauth

commit bbea2006f26de5c8ef9996a8ba13732037f00e37
Author: Catherine O'Neill <cathzozo@gmail.com>
Date:   Fri Sep 12 16:23:55 2014 -0500

    updated sessions_controller_spec to have user gravatar and verified

commit f8bc1afdd2b9005b17d7311c525deee00da47621
Author: Catherine O'Neill <cathzozo@gmail.com>
Date:   Fri Sep 12 16:10:19 2014 -0500

    added gravatar_id to user creation, now passing all tests

commit 2d56e4c314e0f50a12f63a66fa49b0c243a6e617
Author: Catherine O'Neill <cathzozo@gmail.com>
Date:   Fri Sep 12 16:08:11 2014 -0500

    add gravatar id to update_user_spec, now failing 2 tests

commit 411b1891fee921a98d337439af597dd38c094607
Author: Catherine O'Neill <cathzozo@gmail.com>
Date:   Fri Sep 12 16:03:11 2014 -0500

    added gravatar id to get_user_spec, now 1 failing test

commit 18d5f8d716175bde4c074e07366801d8ffe4298f
Author: Catherine O'Neill <cathzozo@gmail.com>
Date:   Fri Sep 12 16:02:47 2014 -0500

    added gravatar id to class_group_controller_spec

commit 39e52cde15fdb823f9ea4f9efebfec75d3f6c99b
Author: Catherine O'Neill <cathzozo@gmail.com>
Date:   Fri Sep 12 15:54:22 2014 -0500

    updated before block in spec for user controller

commit 57503c21d95669745f5e3d8c5322838865b7f0d7
Author: Catherine O'Neill <cathzozo@gmail.com>
Date:   Fri Sep 12 15:29:20 2014 -0500

    added gravatar column to user table in db