add vector<float> to hold vertices/normals/texcoords

also add a getter to retrieve them from model
put VertexBuffer class in a separate file outside of gemvertexbuffer class

thus it can be easily reuse (in [model] for instance)
use VBO to render the model

plugins should fill vector with model data
use vector<vector<float> > instead of vector<float>
don't push color if it's empty
check vector size before filling array
Merge remote-tracking branch 'avilleret/model_plugin'
move VertexBuffer into Gem/

only objectclass implementations should live in Geos/
finalize relocation of VertexBuffer to Gem/
remove #ifdef checks for building modelASSIMP2

we only build this module, if we have assimp2,
so no need to double-check