Merge branch 'develop' into develop-qt
Merge remote-tracking branch 'upstream/develop-qt' into develop-qt
Allow mean altitude calculation on LineStringGraph

* Added a LandRGraph virtual method
* Modified mean altitude calculation on PolygonGraph method
* Added mean altitude calculation on LineStringGraph method
* Uptaded related tests
Merge branch 'develop' into develop-qt
Merge remote-tracking branch 'upstream/develop-qt' into develop-qt
Project opening in OpenFLUID-Builder with Qt

* Added the ability to open and run a project with rough error
management
* Refactored PreferencesManager using QSettings
* Refactored headers for spatial loops, with separated threaded loops
* Modified test name for gtk based tests
* Updated tests

(references OpenFLUID/openfluid#246)