Create the All Signers table in Contribute.

- lists and displays all of the folks who have signed either an ICLA or CCLA.
- changes the menu nav to Contributors instead of Contribute.
- implements User.all_cla_signers
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.
Make Contribute content and sidebar responsive.