Allow asynchronous annotation upload

[Daankrol]

Geti 2.3.2 with SDK 2.3.0

Task Type	Num. Images	Num. Project Labels	Synchronous Duration	Synchronous Speed (a/s)	Async Duration	Async Speed (a/s)	Speedup
classification	100	100	00:00:42	2.37	00:00:25	3.99	1.68
hierarchical_classification_easy	100	82	00:01:21	1.22	00:00:57	1.74	1.43
hierarchical_classification_complex	100	220	00:02:34	0.65	00:02:34	0.65	1.00
detection	100	1	00:00:37	2.65	00:00:19	5.21	1.97

[ljcornel]

Looks good to me, just a minor comment