Refs #5911 Adds function elgg_get_subscriptions_for_container() and equivalent subscriptions service method.
Updated docblock for elgg_get_subscriptions_for_container()
Method getSubscriptionsForContainer() should take a container_guid instead of an entity_guid.
Added a unit test for getSubscriptionsForContainer().
Fixes #2356 - Changed _id suffixes to _guid for variables when relevant
Pass getSubscriptionsForContainer() a guid instead of an entity.
Added a test for getting subscriptions for a container when there are no notification methods registered.
Refs #2356 - Reverts invalid name changes
Merge pull request #6120 from Srokap/ticket_2356

Fixes #2356 - Prefers _guid over _id suffix for variables referring to guids
Merge pull request #6112 from juho-jaakkola/container_subscriptions

Refs #5911 Adds function elgg_get_subscriptions_for_container()
constructor changed on session storage - updated installer