Added collaborators, closes #3

Squashed commit of the following:

commit 52f7d19cf10d68923a4c7c4e2562d13b52378b00
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 12:47:53 2013 -0600

    fixed bug around accounts

commit b7dffa7180cbcccc24f4d80e00fccd46e14172f4
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 12:23:57 2013 -0600

    updates to children index styles

commit c7bd17dc08da11275aac42019f3ebbcade2f66e5
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 12:13:29 2013 -0600

    show all writable children in profile

commit 8b17e2e7dc19d8c4c7a88a45592e8ea73ba46d0d
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 11:54:27 2013 -0600

    added #actions to letter decorator

commit 320652e3d3b85ebf8610767d0b34304e935e2131
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 11:49:13 2013 -0600

    updates to letter policy

commit 8537915265f4df83815573f59605e40ba6b15743
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 11:24:19 2013 -0600

    require a child that is writable, not a child that is owned in Letters#new

commit 4a90cd58f0259f633a42f9033f2eea55183bacc8
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 11:22:34 2013 -0600

    updates to child policy

commit bd2e659c2a4d9067b3780402d9b541d45f0953a7
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 11:22:09 2013 -0600

    added Child.writable_for

commit e53eb2f777958059c3400a7b24c67b09275f09da
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 11:04:50 2013 -0600

    added ability to add collaborators

commit d2e3185595aed093949869342f18bae4a1087b37
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 09:57:02 2013 -0600

    added rails binstubs

commit 90c8451230ecda010af3b8c15c4560ae5343fbc7
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 09:56:54 2013 -0600

    each letter now belongs to a user

commit 65faa39680d79e0138bb5334f14a71bf92d6da68
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 09:56:25 2013 -0600

    fixed seeds

commit d428166e4b75c93fcd0fadae58efd6bc7cae4100
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 09:24:19 2013 -0600

    updated letter_policy for collaborators

commit 89098422f34c03e790dfc30dbef5ab8e64bbf75b
Author: Andrew Thorp <andrewpthorp@gmail.com>
Date:   Wed Nov 20 09:24:05 2013 -0600

    added collaborator relationship
style updates
style updates
added #all_letters_button to child decorator
added content/styles
adds exceptions to github with party_foul, closes #38