Allow spatial connections modifications during simulation stages
Fixed simulation variables usage in KML observer 

* Added ability to take latest available value if no value is available
on current time step
Add of Firespread example project and simulators

(references OpenFLUID/openfluid#20)
Update of Firespread example project and simulators

* Added definitive dataset
* Fixed computation of fire production

(references OpenFLUID/openfluid#20)