gapi: Bring back puppet and langpuppet

This reverts commit e767655ede.

In addition, it applies required changes to function with the new CLI backend.

examples/puppet/langpuppet/graph1.pp

@@ -0,0 +1,10 @@
+class mgmt_first_handover {}
+class mgmt_second_handover {}
+
+include mgmt_first_handover, mgmt_second_handover
+
+Class["mgmt_first_handover"]
+->
+notify { "second message": }
+->
+Class["mgmt_second_handover"]