Display omniauth provider when linking account.

There was no provider param, which left the flash message when connecting an
account a little empty. This adjusts the flash message to use the provider from
the omniauth hash.
Check for Supermarket bucket config using string keys

Magiconf uses string keys not symbol keys so this changes the
CookbookVersion tarball logic to account for that so it works.
Merge pull request #299 from opscode/symbols_are_not_strings

Check for Supermarket bucket config using string keys
Merge pull request #284 from opscode/account_flash

Display omniauth provider in flash when linking account.
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
Initial attempt at implementing API authentication, more to come.
Allow for testing failing uploads.
Test failing auth.
Add additional failure point for auth.
Abstract much of share_cookbook into SignedRequestHelper class for reuse between other authenticated API endpoints.
Start to protect destroying cookbooks.
Get all API specs working except destroy.
Some cleanup.
Make all the API specs pass, finally.
Update cookbook uploads controller specs to handle authentication.
Need to wait for jQuery animation to finish before trying to fill out form.
Clean up and document API helper classes.
Resolve rubocop offenses.
No need for classes anymore for cookbook uploads or signed headers.