devs: fixing recursive delCoupledModel function

The Coordinator::delCoupledModel function in Coordinator does not delete
recursively all children. (closes #33).
gvle: remove unecessary includes

- replace global includes gtkmm.h by includes of specific gtkmm widget used
by gvle (Closes #36)
- remove also some vle unecessary includes
coord: add unit test for recursive deletion

A new unit test of coordinators for deletion of couple model
(Closes #37).