Use grunt to bump versions WIP

Use [`grunt-bump`](https://github.com/vojtajina/grunt-bump) to auto update the versions in `package.json` and `bower.json`. This change also adds the version into `DS.DjangoRESTSerializer.VERSION` and `DS.DjangoRESTAdapter.VERSION`. The version is read out of `package.json` and then incremented. This also removes the `VERSION` file.

The way it is currently configured, `grunt-bump` will auto increment the version, tag with the new version, commit the version bumps. It can also push automatically which might be worth it, but I figured we could talk about it first.

This also removes the gitignore on `dist/` to allow the latest versions of the files to be in the repo for users to access -- is this what we should do?

See https://github.com/toranb/ember-data-django-rest-adapter/issues/75 https://github.com/toranb/ember-data-django-rest-adapter/pull/73 https://github.com/toranb/ember-data-django-rest-adapter/issues/72 https://github.com/toranb/ember-data-django-rest-adapter/issues/71