switch GET api interface to direct interface with elasticsearch

[Dieterbe]

anthracite will be using ES as backend store for the foreseeable future.
anthracite should keep it's own api for put/post requests, because it does validation based on custom schema, and may even need to do certain actions / document modifications based on the data;

but for getting documents, there's no need to create our own API if ES already has a great one.
we want support for searches, date/time ranges etc, so I'm thinking anthracite should just proxy certain requests to ES, based on certain rules, and others (to store documents) it should handle itself.

for now, tools that retrieve events (like timeserieswidget) can just query ES, and i'll figure something out so that you can point to the anthracite url and have it proxy automatically

cc @coreygrunewald