Style CLAs, Emails, Sign in, Sign up

Adds styling for CLAs, CLA notification and invitation emails as well
as signing up and signing in. Maildown was removed in order to support
full HTML/CSS styling of emails. Some feature specs were adjusted to be less
dependant on application text. Also client side validation was added using
Foundation abide.
Merge pull request #103 from opscode/cla-process-ui

CLA invitation, signing and support screens (sign in, sign up, invite accept/decline)