Remove Hound, add ESLint to Travis

[esoterik]

Hound CI has nonstandard rubocop defaults, so currently the style rules it checks for differ from running rubocop locally and on travis. We need to update our rubocop config with either the Hound defaults or the rubocop defaults for consistency.

[esoterik]

This may be a non-issue depending on the results of this issue on Hound

[esoterik]

Currently Hound merges your config with their defaults, so it's probably better to base our rubocop config off of their's

[orenyk]

After further discussion, it seems better to revert to just using our Travis build for style checks and add ESLint there (which I believe is basically #1077, I'll merge that in here). While Hound recommends against running any style checks on an existing codebase (and it's not an invalid point), I think that we'd benefit from cleaning up our limited JS code now across the codebase and then maintaining it in the future.

[esoterik]

blocking on #1579

[esoterik]

unblocking; ESlint will be installed on master first