fixes a speed issue with programmable gl and ofDrawAxis()

this addresses issue #2607

Is there a more elegant way to keep a static version of the axis vbo around?

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>
applies size parameter upon axis mesh creation

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>
change cachedAxisVbo to singleton =)

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>
further cleanup

uses cleaner syntax for cachedAxisVbo.

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>
update to heap-allocated axes mesh

* made cached axes heap-allocated following @arturoc's advice
* fixed typo (correct plural of axis is 'axes')
* added brief doxygen description

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>
Merge pull request #2608 from tgfrerer/fix-GLProgrammableRenderer-ofDrawAxis

Fix gl programmable renderer of draw axis