adds fixed function vertex attributes

+ leaves programmable path as is (everything but for indices is an attribute)
+ adds fixed function vertex attributes for fixed function pipeline
+ this keeps the promise intact that a buffer location == shader attrib location
+ keeps the programmable path clean so that when we deprecate the fixed function pipeline eventually, we can do this by only removing a couple of if branches.
+ caches programmable renderer test for speed and stability
better caching for isProgrammable

+ query isProgrammable once, keep as static bool for all to see.
+ since it's impossible to have a fixed function and a programmable context within one app, the check only needs to happen once, even a rendererCollection must be homogenous in this respect.
update checks for fixed function renderer

+ makes sure fixed function renderer checks for usingVerts rather than the position attribute when issuing draw commands.
+ uses fixedFunctionPositionAttribute to draw when using fixed function.
add vao checks to fixed function helper methods

+ ensure VAO availability is checked before helper methods set vbo data
fix renderer check

+ ensures renderer check only happens *after* renderer has been initialised.

Since there are lots of static `ofVbos` and `ofVboMesh`es floating around, these get initialised before the actual renderer does. This makes sure to perform the renderer check only after the renderer has been initialised.
fix const getters
fix missing location setting in setAttributeBuffer
changelog update

add entry for ofVbo refactor
Merge pull request #3379 from tgfrerer/fix-fixed-function-vbo-attrib

Fix fixed function vbo attrib