[#120] Add iati-identifier filter
[#120] Add unit test for  iati-identifier filter
[#120] Add last-updated-datetime filter
[#120] Add registry dataset filter
Merge branch 'master' into 120-new-filters
Merge branch 'master' into 120-new-filters
[#120] Add provider/receiver activity id filters
[#120] Add documentation for new filters
added provider_org_activity_id filter
Merge branch '120-new-filters' of github.com:xriss/iati-datastore into 120-new-filters

Conflicts:
	iati_datastore/iatilib/frontend/dsfilter.py