Allow modules to easily register reports, payprocs, and searches

The extensions system currently allows one to create an extension which is either a single report-template, a single payment processor types, a single custom-search, or a module. However, it is hard to package together several related bits – e.g. a payment processor which also uses hooks, or a set of related reports.

To resolve this, we will make it easy for any module – Civi module, Drupal module, etc – to register report-templates, payment-processor types, and custom-searches via hook. Module authors will be responsible for declaring any metadata that goes along with their classes – but inserting, updating, deactivating, and deleting metadata from the DB will be handled automatically.

Major pieces of this puzzle:

• Add APIs for CRUD'ing report-templates, payment-processor types, and custom-searches
• Add mechanism to determine which modules are enabled, disabled, or uninstalled
• Add hook_civicrm_managed which accepts API data structures for declaring managed objects. A managed object is one that is automatically inserted, updated, deactivated, deleted based on its module's status.
• Add table civicrm_managed for tracking which objects are managed – and which modules own them
• e.g. civicrm_managed(module varchar, name varchar, entity_type varchar, entity_id int)
  *Every time the cache is cleared, call hook_civicrm_managed and reconcile the list of managed objects.
• A coding convention in civix for using these pieces