Add NamedTransform option to ocioconvert tool.

[pennelee]

Added two uage options to ocioconvert to apply NamedTransforms:

ocioconvert [options] --namedtransform transformname inputimage outputimage ocioconvert [options] --invnamedtransform transformname inputimage outputimage

--namedtransform Convert using a named transform in the forward direction --invnamedtransform Convert using a named transform in the inverse direction

Tested with cpu, gpu, gpulegacy on named transforms from OCIO configs (studio-config-v2.1.0_aces-v1.3_ocio-v2.3.ocio, cg-config-v2.1.0_aces-v1.3_ocio-v2.3.ocio) with various resolution EXR files (640x426, 1280x853, 1920x1280, 5182x3456).