Add support for Adam, Adafactor, and RMSprop optimizers, implement GL… #269

Job	Run time
Specialised + canvas smoke	17s
Preset matrix (smoke, ubuntu) (4)	9s
Preset matrix (smoke, ubuntu) (3)	17s
Preset matrix (smoke, ubuntu) (2)	11s
Preset matrix (smoke, ubuntu) (1)	16s
Mini-train matrix (macOS, nightly)	0s
Matrix report	9s
	1m 19s

Provide feedback