[#224] Add benchmarks to XSLT

Add selectors under result/indicator that turn into RSR benchmarks.
[#224] Add IATIBenchmarkResource

Add IATIBenchmarkResource to be able to process indicators in the IATI
XML and turn them into RSR benchmarks.
[#224] Add IATICategoryResource

Add IATICategoryResource to be able to create Project.categories
correctly from the IATI XML.
[#224] Add new resources to api/resources/__init__py
[#224] Remove org creation when posting IATI XML

Since all organisations now are created by an external script to
include more data about them, stop creating organistions from XML data
and instead raise an exception.
[#224] Add IATIProjectResource.benchmarks and
IATIProjectResource.categories

Add new toManyFields to IATIBenchmarkResource and IATICategoryResource

Extend alter_deserialized_detail_data() to massage the data needed for
the new fields
[#224] Better log output from the cordaid IATI XML loader script

The script now only uploads data for new projects.