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.
Use gravatar for author and committer avatars.
Merge pull request #267 from simi/commit-gravatars

Use gravatar for author and committer avatars.
Remove unnecessary ; from spec_helper.
Show committer in build header only when he's not author.
Merge pull request #268 from simi/show-committer-only-when-needed

Show committer only when needed.
Update jobs summary to new format.
Merge pull request #269 from simi/update-jobs-summary

Update jobs summary to new format.
Fix font in the "Sync Now" button.
Don't break the branch name.

If it's too long, we'll hide the rest.
Fine tuning for branch name and subject.

In Chrome, it looked slightly off, the line-height adjustment
seems to fix it.