CpuGLVB: reading data back from the GPU each time model is changed is not very efficient.
Model the GL VB after D3D11 one, where there are no data read backs, however this means
an extra memory copy of the buffer. 4th level uniform subdiv on Car, glGetBufferSubData
was taking 50% of CPU time before (actual subdiv 22%), now that is gone. Full CPU Draw
62ms -> 54ms, looks like most of overhead now is just waiting on GL queries).
glViewer: line widths larger than 1.0 are deprecated in core GL (generates a GL error)
glViewer: don't generate GL errors with invalid UBO indices (happens on OSX since tessellation is not supported)
glViewer: set sync off on all platforms
CpuGLVB: dirty flag to not keep on uploading if data did not change
CpuGLVB: code review changes
Merge pull request #109 from aras-p/glvbo-fixes

CpuGLVertexBuffer performance fix + glViewer fixes

reviewed, approved & much appreciated : thank you

takahito + manuelk