Incomplete or unnecessary settings

[shinya7y]

Issue 1: warning of size mismatch and unexpected key in inferring the provided COCO weights
Solution 1: set num_layers=2 in pos_cfg

Issue 2: dcn_on_last_conv in ATSSHead
Solution 2: modify atss_head.py

Issue 3: some settings are unsupported in mmdetection (e.g., GlobalWandbLoggerHook, backend='zip') #8
Solution 3: clean configs

I hope the commits below help fix.
shinya7y/UniverseNet@9079cfc
shinya7y/UniverseNet@44deecc