[#710] Add filtering on ID for ProjectResource
[#710] Add selector to find internal project ID for RAIN activities
[#710] Improve ImageImporter.get_from_url()

Add exception handling when Requester throws an exception.

Set ImageImporter.filename. This is used when generating the file name
when saving the image to a django model.
[#710] Import Requester and IamgeImporter from api_utils
[#710] Add RainActivity class

RainActivity is used to map data in the IATI activity to RSR fields. It
is used in rain_project_upload.py and post_import.py.
[#710] Remove debug break point
[#710] Add identify_rsr_project()

identify_rsr_project() queries the RSR API to find a project using
1) the RSR ID, 2) the IATI ID and 3) the RAIN internal ID if available.

If a project is found in multiple ways it also asserts that it is the
same project that is found by all methods.

Modify upload_activities() to use identify_rsr_project() and the
RainActivity class.
[#710] Better logging for post_import.py