Replace tslint with eslint

[sprucely]

There are still a lot of warnings, most of which will require declaring interfaces and function return types.

[srkirkland]

Looks pretty clean, I'll test it out

[srkirkland]

I think we'll need to tweak some of the rules since they seem pretty harsh (no explicit any?), but since we aren't failing builds based on linting yet then I think we can keep these best practice rules for now and then update on an individual basis instead of trying to recreate our old rules. I do like this setup though and the code changes you've made seem to work well.