After migrating to eslint some errors were disabled to make it easier to
migrate.
This enables all the lint rules and treats all warnings as a build
failure. Similarly, CI won't automatically try to fix mistakes.
Change-Id: Iff9c4a59401900fc395cd566dd328f3a9c688a12
tslint has been deprecated so it's nice to switch to eslint.
Currently this uses a minimal eslint, to get things up and running.
node-sass requires C which does not work nicely on all platforms.
Change-Id: Icf12e375293e052befc2d0daeb23d73697ed6ded