Adding documentation on intermediate throwing compensation events - restructured section, adding paragraph about process variable snapshots

Adding documentation on intermediate throwing compensation events - adding additional note illustrated by an example process

ACT-1107: Added docs and execution listeners to intermediate throw none event including parse listener (for KPI support)

ACT-1103 adding testcase verifying that the PVM is able to start a process instance at an alternative initial

ACT-1092 adding support for querying for bpmn signal event subscriptions and triggering the signal from outside