Show coverage percentages in table of contents

Summary:
Rough cut -- this needs style / color / tooltips, etc. Show raw coverage and "modified coverage" (coverage on lines you touched) in the table of contents.

https://secure.phabricator.com/file/data/id3apce5p5gevkee6tg2/PHID-FILE-kxcxlbsej454t4xiht2o/Screen_Shot_2012-03-12_at_3.30.30_PM.png

Test Plan: See screenshot above.

Reviewers: tuomaspelkonen, btrahan, zeeg

Reviewed By: tuomaspelkonen

CC: aran, epriestley

Maniphest Tasks: T965

Differential Revision: https://secure.phabricator.com/D1864