Add support for versioned API

This MR restructures the way the views are implemented to allow for a versioned API. This should allow us to implement a new version of the API to better support future query types whilst still supporting legacy clients.

I have plans to write up a V2 of the API that better supports multiple file formats, so this is the first step.

This should have zero impact on functionality, and so should support queries from the current client.

gwdatafind_server/api/v1.py

@@ -2,7 +2,10 @@
 # Copyright (2019) Cardiff University
 # Licensed under GPLv3+ - see LICENSE
 
-"""REST API views for GWDataFindServer
+"""GWDataFind API v1
+
+This API provides the same endpoints as the 'original'
+LDR DataFind server API.
 """
 
 import json