Use SpatialHarvester from ckanext-spatial as base for harvesters
Move CSW, WAF and doc harvesters to ckanext-spatial

They are now the default harvesters for these sources. WAF Collections
and z3950 harvesters are project specific for the time being.
Readd custom harvesters for CSW, WAF and Doc sources

But now they only add a transform_to_iso method to be able to
handle FGDC records.
Update get_extra calls to self._get_object_extra
Merge branch 'master' into move-harvesters-to-spatial

Conflicts:
	ckanext/geodatagov/harvesters/__init__.py
Minor fixes to ArcGIS harvester for new base harvester
Merge branch 'move-harvesters-to-spatial'