[#381] Add script to migrate creation times from django_admin_log to
created_at fields for Organistioan and Project

The script looks for ADDITION event in the django_admin_log and copies
the time of the event to the created_at field for the object.
[#381] Fix API field names for ProjectUpdate.created_at and
ProjectUpdate.last_modified_at in the API

To keep the API signature from changing the timestamp fields for
ProjectUpdate are exposed with their old names "time" and
"time_last_updted" in /api/v1/the project_update API resource.
#381 attempted adding Partnersite Timestampe and moved Org and Project fields
[#445]include DB migration script
[#381] Fix problem with timestamp fields for PartnerSites

The admin broke when timestamp fields were added to PartnerSites using
the Timestamp mixin. The reason for this is that the fields have the
attributes auto_now_add and auto_now. Having auto values thay are
excluded from the form. Adding them to readonly_fields adds them back
again.
[#381] Add label to timestamp fields and fieldset for ProjectUpdate

Add a label, "Timestamps", to the field section for timestamp fields
for Organisation, Project, ProjectUpdate, and PartnerSite.

Add a fieldset to ProjectUpdate to organize the fields and to be able
to show the timestamp fields since they need to be part of the
readonly_fields attribute.
[#381] Add migration for timestamps for PartnerSite
Merge pull request #446 from akvo/feature/381_timestamp_fields

Feature/381 timestamp fields