Fixed forceVBO in Mesh

At least one recent commit https://github.com/libgdx/libgdx/commit/7020231ca8b1e14995d398603de525581e3d1282 has completely disabled VBO support in the SpriteBatch class for not so clear reasons. 
My project uses GL20 for now only and I would like to use/test VBOs, so at least there's a way to bring back VBOs in spritebatch by using the forceVBO flag.

Also one thing not taken into account in the SpriteBatch class is culling with GL_CULL_FACE. Spritebatch uses a (non default) CW front face order (default is CCW as front face), which makes things a little bit uneasy if you have mixed usage with other custom CCW meshes.

If someone could clarify why SpriteBatch was changed I would appreciate as well. 
Reason being is that setting a new texture for every draw can be the cause of the slow down instead of the vbo itself. 
Eg: Some engines can sort the meshes by material before drawing, minimizing state changes for performance reasons.