Besides removing unnecessary imports, this also fixes the missing logger module in test_architectures.py within the static directory.

* add solov2 enhance model

* fix for_mot in PPYOLOTinyFPN and PPYOLOPAN

* fix yolo_fpn

* add fairmot

* rename pretrain_weights

* add comments; reuse focal loss and convnorm

* update comments

* jde and deepsort: model

* fix name of ConvNormLayer for fcos solov2

* fix name in other head convbn

* fix yolo name, fix ttf_head name, test=document_fix

* add ttfnet enhance

* add doc

* fix pafnet training

* add ppyolov2

* fix bugs and modify docs

* modify code and doc according to review

* fix bugs while resolving conflicts

* add PP-YOLO tiny

* add senet

* add annotations according to review

* add fcos ttfnet coment, update modelzoo

* fix ttfnet coment