Merge pull request #56 from DavidBruant/master

mergeable PR. Supersedes #54
renaming + attempt at better robustness when loading binary objects
refactoring loadObjects to call scene.add and scene.remove only when necessary
Merge pull request #57 from DavidBruant/optimz

Optimz
display shadows on startup (used to work only when hour was changed from gui) + mutualizing material among geometries