Supports optional licenseBranch field

Fixes #82 by adding an optional licenseBranch field to the projects.yml
file. If specified, a project's license can be linked to a specific branch
by adding a field:

```
licenseBranch:
  repo_name: branch_name
```

If not specified the default, master, will be used.
Addsif statements to only show impact and partners when they exist. Adds detection for one or multiple clients to change s or no s in partners. Changes clients in yml to array so can do that detection. Changes layout on project pages to accomodate this new info. Adds place for secondary partners.
Fixes spacing on licenses if they go onto a new line. Fixes spacing between repos if there is more than one. Attempts and fails to add project plural or not to dashboard home, but leaves note to team to figure out with help later.
More small changes.
Adds conditional statement to milestones div.
Fixes the partner/partners problem on the home page
Initial commit of status description page.
Fixes missing page problem.
Removes index page styling that is unnecessary on the stage description page.
Fixes responsive sizing bug.
Merge branch 'gh-pages' of github.com:18F/dashboard into gh-pages