adding eslint to project

[charliewilco]

Addresses #596.

• adds eslint to project
• jscs rules don't match one for one to eslint so that isn't an exact match for current linting set so i'm hoping for feedback on this PR

Other considerations

• removing jscs
• disabling jshint in favor of eslint

cc @HospitalRun/core-maintainers

[jkleinsc]

@charlespeters thanks for the PR! Looking at https://github.com/DockYard/eslint-plugin-ember-suave it appears that it is still in progress and I would like to wait until that is stable to move over. I'm ok leaving this PR open until that happens.

[jkleinsc]

@charlespeters it looks like https://github.com/DockYard/eslint-plugin-ember-suave is ready to use:
https://dockyard.com/blog/2016/09/30/retiring-ember-suave

Would you be willing to update this PR so that we can move from ember-suave? Thanks!

[charliewilco]

@jkleinsc now the fun part of this is that now we're using eslint, some of the tests are failing.