[performance] Use vertex array objects where available

[Sam Spilsbury]

Currently, every time we want to render something we have to do something like this:

glBindBuffer (GL_ARRAY_BUFFER, vertices);
glEnableVertexAttribArray (verticesLocation);
glBindBuffer (GL_ARRAY_BUFFER, colors);
glEnableVertexAttribArray (colorLocation);
glBindBuffer (GL_ARRAY_BUFFER, texcoords);
glEnableVertexAttribArray (texcoordsLocation);

glDrawArrays ...

glDisableVertexAttribArray ...

glBindBuffer (GL_ARRAY_BUFFER, 0);

With vertex array objects we can do this:

glBindVertexArray (vArray)
glDrawArrays

Much fewer calls into openGL! And much fewer expensive ones too.