[#451] Add org_data_from_xml()

org_data_from_xml() is a more general way to get from the etree
representation of the data to the dictionary needed in the Django ORM.

The core idea is to use an initial dict that holds the Organisation
field names as keys and the xpath expressions for getting the data from
the etree as values. After running the xpath part using calls to
data_from_xpaths() post processing of fields that need to be transformed
from the raw data is made.
[#451] Add update_organisation() and add logging for creation of
internal ID

update_organisation() updates an exising organisation with the data
from the XML. This was missing from the previous version of pre_import.

Also add logging for when an InternalOrganisationID is created and
refactor create_new_organisation() to use org_data_from_xml().
[#451] PEP 8 edits

Remove space around "=" in calls to dict()
Merge pull request #454 from akvo/feature/451_update_cordaid_orgs

Feature/451 update cordaid orgs - Looks good to me, I at least understand what the code does, and this is looking tidy.