Flesh out the content on the welcome page.

This is not the final design and content of the Welcome page. It is an attempt
to make it more useful by adding in relevant content that may be useful to new
users and those viewing the application.

- Add three columns of content, for explore, learn and share.
- Add Sign Up button to the welcome page.
Merge pull request #290 from opscode/welcome_page_updates

Add content to the Welcome page
adding owners and collaborators
adding controllers and specs
adjusting routes and adding specs
use jbuilder for this
add select2 for picking collaborators
stop messing with the routes
users should have icla signatures to be collaborators
make the views work
fixing specs
these are useless
collaborators can remove themselves
put the helper back
fixing specs and rubocop offences
adding a mailer for collaborators
didn't need this
Specify the cookbook owner in the db seeds.

When rake db:seed is run, the owner gets set to the user created in the seeds.
This allows cookbook show to function as expected because a user is required.

The ordering of the seeds changed to have users be created before cookbooks, so
the association could be made.
remove the helper to reduce duplication
use an authorizer instead