Allow mailer URLs to have protocol specified

You cannot rely on email clients handling URLs without a protocol
specified correctly. So this allows a protocol to be specified
(generally either http or https) so a full absolute URL can be
generated. This issue originally reared its head by not routing to
images correctly in most email clients.
Display empty content on Manage Profile > Collabs.

When a user is not a collaborator on any cookbooks, display some information
that let's them know here is where they would appear.
Merge pull request #491 from opscode/manage_profile_no_collabs

Display empty content on Manage Profile > Collabs.
Merge pull request #493 from opscode/fix-mailer-images

Allow mailer URLs to have protocol specified
Add closing p tags to Manage Profile > Agreements.
Create the contribute sidebar and styles.

When viewing the contribute tables, display a sidebar with the list of repos
that Supermarket watches aka Chef's open source projects, and if the user is
signed in, display user-specific information about their agreeemnts.
Create the Become a Contributor page

This re-organizes the file structure of where the contribute/sidebar is located,
while creating the route, controller action and spec for the page to point
people to in order to understand what it means to become a contributor.

The content is not ready in this commit, but the framework is there.
[wip] Create the All Signers table in Contribute.

This lists and displays all of the folks who have signed either an ICLA or CCLA.
This also changed the menu nav to Contributors instead of Contribute.
This also implements User.all_cla_signers, which is not complete at this time.

todo:

- improve the User.all_cla_signers method
- improve the all signers table by listing date of signature and adding
  denotation for those who are CCLA signers or ICLA signers or both
Scale all elements' font-size for media queries.

Create a more uniform responsive scaling of text elements by changing the
font-size for all text elements. Previously, p, li, span and blockquote elements
were not being scaled which caused disproportionate sizes of text.
Expand upon the Become a Contribute page.

Add in info and content that explains the steps to becoming a contributor.
Store location for Become a Contributor.

When a user links their GitHub account, redirect them back to
become-a-contributor to keep them on the path to becoming a contributor.