Add trigger_id attribute to the 'assembly' db object

Also impact this changes on API object and add method to get an
assembly by its trigger_id
Added migration script also

Change-Id: I4c4f99ec4083f2620abb231f77b3f76ab19da027
Delegate to the handler when a trigger is posted

Change-Id: I040d207d57bb7b85082745c2ac9940b5b9c1f441
Merge "Add trigger_id attribute to the 'assembly' db object"
Merge "Delegate to the handler when a trigger is posted"