adding jsonld frame endpoint to es-model service

[jrmerz]

Adding a /frame POST endpoint to model service.

{
  "document" : {},
  "frame" : {}
}

Where document is the jsonld document you wish to frame and frame is the jsonld frame you wish to use.

We can discuss location, but model seemed best fit for current setup as it has to do with data transform and isn't part of the public api. But easy to move.