Adds first version of CW Admin Branding plugin

Plugin removes default WordPress branding on login page, in admin nav
bar, and in admin footer. Replaces these instances with Crane|West
branding.

- To customize this plugin for your websites, you should only have to
overwrite cw-admin-branding/images/login_logo.png with client logo.
Image should be 320 px wide, but css should contain larger images.