Solve #863

[j3r3m1]

This PR solves #863:

• OSM buildings having no nb_lev information but building height < 3 m (and >0 m) are now considered as buildings (a new building having these properties has been added in the Redon sample)
• modify the algorithm used to update building nb_lev after building height estimation. However, this fix is not perfect. Ideally, the same algorithm than for the formatting should be used to have a consistency of the method... --> a new issue should be opened or directly solved following this fix ?

Plus ideally, the formatHeightsAndNbLevels should be identical in BDTopo and OSM.