Save information that data were exported

Created by: scardinius

Because of GDPR rules we have to save information that some data were exported. Those could be contact, activity or contribution objects.

I'm going to prepare solution for action "Export contacts", "Export actiivities" etc. Each exported object will have a new type activity, for example "Contact exported", "Activity exported" with additional fields as id of object, subject, who exported.

It's necessary to use new type of hook, because hook_civicrm_export doesn't have ids of objects https://github.com/scardinius/civicrm-core/commit/f46c37304de63001b7da3f62ac15d12eb32d6446

So at this branch caltha-eu:dev-157 is my proposal https://github.com/veda-consulting/uk.co.vedaconsulting.gdpr/compare/master...caltha-eu:dev-157?expand=1