#42 Add ESLint support with grunt-eslint [WIP]

In reference to #42 (and https://github.com/phase2/grunt-drupal-tasks/issues/42#issuecomment-64136831), this is what ESLint support might look like. The included .eslintrc is from https://www.drupal.org/node/1955232.

Note that these example settings may not be the "best" for validating JS in the context of what grunt-drupal-tasks is trying to provide. They are agreed upon for D8, but whether or not they should be the suggested defaults for all Drupal projects is probably up for debate.