Add base class for ArcGIS Open Data v2 API

[chris48s]

There are a number of councils where we are calling https://opendata.arcgis.com/api/v2/datasets to identify new data e.g:

• https://opendata.arcgis.com/api/v2/datasets?filter%5Bcatalogs%5D=data-moray.opendata.arcgis.com&include=organizations%2Cgroups&page%5Bnumber%5D=1&page%5Bsize%5D=10&q=polling&sort=-updatedAt
• https://opendata.arcgis.com/api/v2/datasets?filter%5Bcatalogs%5D=maps-south-ayrshire.opendata.arcgis.com&include=organizations%2Cgroups&page%5Bnumber%5D=1&page%5Bsize%5D=10&q=polling&sort=-updatedAt
• https://opendata.arcgis.com/api/v2/datasets?filter%5Btags%5D=Elections&filter%5Bcatalogs%5D=maps-broxtowe.opendata.arcgis.com&include=organizations%2Cgroups&page%5Bnumber%5D=1&page%5Bsize%5D=10&sort=-updatedAt
• http://gis-pkc.opendata.arcgis.com/datasets.json?q=polling&sort_by=-updatedAt

At the moment we just pass a general query and sync the data to GH so we can check a diff when something changes. If it changes, we know to update the scrapers. It would be useful to add a base class like we have for CKAN and Datapress that can parse that data a bit more intelligently and do it for us.

Tunbridge Wells is a starting point for this:

https://github.com/wdiv-scrapers/DC-PollingStations-TunbridgeWells/blob/master/scraper.py

[GeoWill]

This should probably be v3 now. Cheatsheet: https://gist.github.com/jgravois/1b7ec5080e992a59f65cf7a2190e4365