[#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