Bug 1090689 - Add MPL2.0 headers to the repo

This work fixes part1 of Bugzilla bug [1090689](https://bugzilla.mozilla.org/show_bug.cgi?id=1090689).

This adds MPL2.0 headers to all the relevant files in the treeherder-ui repo. The outliers in the list were done manually, and are the first five in the commit:

Gruntfile.js
docs/Makefile
docs/conf.py
webapp/app/css/logviewer.css
webapp/app/css/treeherder.css

The .bat and .sh scripts in `webapp/scripts` I did not include, since they did not look directly created by us.

Other than those, the remainder were added via a list agreed on in the bug with @edmorley and injected en masse.

Cursorily tested on Windows:
FF Release **33.0.2**
Chrome Latest Release **38.0.2125.111 m**

Adding @edmorley and/or @wlach for review.