Add mosaic meta to /mosaics and /models endpoints

The endpoint `/mosaics` is returning ids only, requiring additional requests to `/mosaics/:id` endpoint to fetch metadata. It would be nice to change `/mosaics` endpoint to include all metadata from mosaics to avoid this flow in the front end. This is a breaking API change.

Another enhancement required by [multiple imagery selection](https://github.com/developmentseed/pearl-frontend/issues/22) in the front end is to include a property `imagery_id` to the `model.meta` object of `/models` endpoint, which will allow matching base imagery of a model.

cc @geohacker @ingalls