Extend LinkView to allow click tracking.

Allows us to hook in to certain links and see how they're used.
Initial version of a new build header.

Based on @Juice10's original designs at travis-ci/travis-assets#24.
Underline links in the commit body.
Add footer section for commit and author details.
Shorter commits for compare URLs, optimize footer.

The flow when reducing the browser width isn't fully right yet,
but we're getting there.
Fix compare link text for tags.
Delete old summary, fix tests for the builds page.

This commit breaks tests for the job page, but bear with me. It
doesn't have the new layout yet.
Change summary on job page, fix more tests.

This brings both pages on par, though the duplication isn't ideal.
Improve spacing for octocats.
Merge pull request #266 from travis-ci/mm-build-header

New summary header
Slightly increased font size for times.