Support IQMs with joints and no poses
Add support for IQM int blend indices and float blend weights

Integer blend indices are converted to bytes at load, ioq3 doesn't allow more than 128 joints.

Heavily based on code by @zippers.
IQM int/float vertex arrays were already swapped
Fix IQM comments refering to IQM_BYTE instead of IQM_UBYTE
Initialize blendIndexesType and blendWeightsType
Merge last two commits into renderergl2
Merge remote-tracking branch 'ioquake3/master'