CiviCRM Core searches should respect campaign hierarchy

[bjendres]

The CiviCRM Core is agnostic towards the campaign hierarchy, despite the fact that the parent_id field is part of core.

I talked to @totten and the desired approach would be:

• create a new setting in the Campaign component: use hierarchy
• the setting has three states:
  • 0: hierarchy will not be used, everything stays the way it is now
  • 1: hierarchy will be used, see below
  • empty: default, will be interpreted as 0
  • Our extension is allowed to set the setting to 1 during install, if it is still empty - i.e. it hasn't been actively set to 0
• We'll create a Core-PR:
  • Adding a function to get the IDs of all children of a campaign. Cached (static variable) if not requested otherwise
  • Adjusting the following searches, basically replacing WHERE ... campaign_id = cid sections with WHERE ... campaign_id IN ({cids}) if the setting is 1:
  • Contribution
  • Activity
  • Event
  • Mailing
  • Participant
  • Pledge