add cascade rcnn on VOC

configs/pascal_voc/cascade_rcnn_r101_fpn_1x_voc0712.py

+_base_ = './cascade_rcnn_r50_fpn_1x_voc0712.py'
+model = dict(
+    backbone=dict(
+        depth=101,
+        init_cfg=dict(type='Pretrained',
+                      checkpoint='torchvision://resnet101')))

configs/pascal_voc/cascade_rcnn_r50_fpn_1x_voc0712.py

+_base_ = [
+    '../_base_/models/cascade_rcnn_r50_fpn.py',
+    '../_base_/datasets/voc0712.py',
+    '../_base_/schedules/schedule_1x.py', '../_base_/default_runtime.py'
+]
+
+model = dict(roi_head=dict(bbox_head=dict(num_classes=20)))
+# optimizer
+optimizer = dict(type='SGD', lr=0.01, momentum=0.9, weight_decay=0.0001)
+optimizer_config = dict(grad_clip=None)
+# learning policy
+# actual epoch = 3 * 3 = 9
+lr_config = dict(policy='step', step=[3])
+# runtime settings
+runner = dict(
+    type='EpochBasedRunner', max_epochs=4)  # actual epoch = 4 * 3 = 12
+

configs/pascal_voc/faster_rcnn_r101_fpn_1x_voc0712.py

+_base_ = [
+    '../_base_/models/faster_rcnn_r50_fpn.py', '../_base_/datasets/voc0712.py',
+    '../_base_/default_runtime.py'
+]
+model = dict(
+    backbone=dict(
+        depth=101,
+        init_cfg=dict(type='Pretrained',
+                      checkpoint='torchvision://resnet101')),
+    roi_head=dict(bbox_head=dict(num_classes=20)))
+
+# optimizer
+optimizer = dict(type='SGD', lr=0.01, momentum=0.9, weight_decay=0.0001)
+optimizer_config = dict(grad_clip=None)
+# learning policy
+# actual epoch = 3 * 3 = 9
+lr_config = dict(policy='step', step=[3])
+# runtime settings
+runner = dict(
+    type='EpochBasedRunner', max_epochs=4)  # actual epoch = 4 * 3 = 12