MOTECH-589 Add case-related fields to the "Received form" triggers

The presence of the case related fields in Form XML depends on
the settings at the CommCareHQ side, which I believe we cannot access.
Therefore, if the setting is not to use cases, the case related
fields will be empty.

Change-Id: I5ffc3b259637a799ababa29ec8ec8937a7476456
Merge "MOTECH-589 Add case-related fields to the "Received form" triggers"