Update HydroShare Resource in Backend

[rajadain]

Currently, POSTing to an existing HydroShare resource simply returns the current value, instead of updating it:

model-my-watershed/src/mmw/apps/export/views.py

Lines 59 to 65 in 9b10846

	# TODO POSTing to an existing export should update the resource
	# Currently it is just paired with GET
	# GET existing resource simply returns it
	if hsresource and request.method in ['GET', 'POST']:
	serializer = HydroShareResourceSerializer(hsresource)
	return Response(serializer.data)

Instead, it should update the resource. Currently, it does not seem possible to update the resource via the hs_restclient, although such may be possible via the REST API itself. However, we should only need to focus on updating the files (GMS, and whatever format is decided for TR-55 projects). This can readily be done with deleteResourceFile and addResourceFile.

Optionally, the resource can also be versioned, to indicate new changes, like this:

hs.resource('RESOURCE ID').version()