Changes in actions

[stefanopet91]

The actions section of the schema has been changed (https://github.com/netgroup-polito/nffg-library/blob/master/schema.json).
In particular, "output" has been renamed to "output_to_port" (string) while "output_to_controller" (boolean), "drop" (boolean) and "push_vlan" (string) have been added.
I ask you, if it's possibile, to modify the json renaming "output".
"drop", "output_to_controller" and "push_vlan" should be added to the graphical creation of flowrules considering their type (string or boolean). Also "pop_vlan" thas is present, should be changed to a boolean value. Referring to #11, default value of boolean fields is false and they should be present in the json only if true.
Is it possible to dynamically read fileds and types from the schema, avoiding to modify the code every time there is a change?
Thank you and sorry for all these requests 😄