Bugzilla

Currently, to run the messaging system / new tab unit tests and sasslint in mozilla-central, one has to use a few npm commands, documented on [firefox-source-docs](https://firefox-source-docs.mozilla.org/browser/components/newtab/docs/index.html).  These should really just run automatically when using `mach test` on/in the appropriate directory.  If we stick with SASS, we might well want to move that piece into `mach lint`, but just getting them running at all using one of the basic `mach` commands is the most important first step.