[FEATURE] Send end event to client when an ASYNCAGI BREAK is executed on Asterisk

Not complete as this is currently a breaking change. Needs the addition of a check for a channel variable to switch on this behaviour.
Merge branch 'develop' into feature/ast_return_to_dialplan

Conflicts:
	lib/punchblock/translator/asterisk/component/asterisk/agi_command.rb
[CS] Require channel var to be set to enable dialplan-handoff behaviour

PUNCHBLOCK_END_ON_ASYNCAGI_BREAK

This ensures backward compatibility and finishes #139
Merge branch 'feature/ast_return_to_dialplan' into develop