[#381 #458] Display timestamps in the admin for relevant models
[#381 #458] Display timestamps in the admin for relevant models

Using the TimestampsAdminDisplayMixin add the display of timestamp
fields to Organisation, Project, ProjectUpdate and PartnerSite model
admins.

Change where the fields are displayed to kill bug #458 that happened
when the timestamp fields had their own fieldset that was only shown
when there was any timestamp data.

akvo/akvo-rsr,akvo/akvo-rsr,akvo/akvo-rsr,akvo/akvo-rsr