Replace memory batch size with a fraction of the total batch size #616

Job	Run time
prepare	6s
tests (avalanche-er.json) / run	5m 10s
tests (avalanche-lwf.json) / run	3m 45s
tests (avalanche-ewc.json) / run	4m 31s
tests (avalanche-icarl.json) / run	4m 11s
tests (cls-er.json) / run	4m 18s
tests (der.json) / run	5m 32s
tests (er.json) / run	5m 23s
tests (fine-tuning.json) / run	3m 27s
tests (gdumb.json) / run	4m 4s
tests (joint.json) / run	5m 21s
tests (offline-er.json) / run	5m 24s
tests (pod-er.json) / run	8m 16s
tests (super-er.json) / run	4m 53s
	1h 4m 21s

Provide feedback