Fix for extensions release and close in OpenFLUID-Builder

* Added a releaseAllExtensions() in registry, 
  called at ProjectModule destructor
* Updated CMake macros for installation of builder extensions
* Switched to version 2.0.0~beta14
Add of an extension for viewing spatial graph in OpenFLUID-Builder

* Added workspace extension with simple graph viewing and exporting
  capabilities

(references OpenFLUID/openfluid#6)