Serrano

**Bugs**
- 229 - Fix (add) support for query processor on the contexts endpoint
- 9c72382 - Ensure request is passed into `processor.get_iterable` in preview endpoint

**Bugs**
- 221 - The requesting user was not be supplied when determining which data fields and concepts should be returned to be viewed. This fix depended on cbmi/avocado253 which incorporates a new setting to toggle the behavior of object-level permissions.

**Changes**
- Update minimum version of restlib2 to 0.4.2 which ensures JSON is decoded from the request body as UTF-8 rather than ASCII.

**Bugs**
- 213 - Fixes an issue that improperly decoded UTF-8 data as ASCII when sharing a query.

**Changes**
- Serrano now overrides the default `DataConcept` formatter with one that includes a `to_html` method which works better with the `/api/data/preview/` endpoint.

**Bugs**
- Fixed a bug when requesting all values for a field when no values existed.

**Enhancements**
- 200 - Add support for the `processor` GET parameter (introduced in 2.3.6) for the `CountStats` resource
- 199 - Introduce `STATS_CAPABLE` setting which is a function that takes a `DataField` instance and return true is links to the stats resources should be made available to clients.
- 207 - Add support for a message when sharing a query.

**Features**
- 190 - Add new _stats_ root endpoint and default _count_ endpoint for calculating the number of distinct records for all visible models
- This is useful for reporting on the of records per type available in the application
- 192 - Add support for the `processor` URL parameter for choosing which Avocado query processor to use in the resource

**Enhancements**
- 185 - Improve performance for getting random set of data field values
- 193 - Add support for a `STATS_CAPABLE` setting which is a function that takes a `DataField` instance and returns a boolean to whether it should support the `/field/<pk>/stats/` endpoints.
- 195 - Write operations now mark the session as modified to prevent active sessions from expiring

**Bugs**
- 184 - Account for non-root deployments for shared query URLs