RC LOWBR mode merge
avoid QP sudden fluctates
add UT for PredMv in decoder
Merge pull request #559 from huili2/UT_PredMv

add UT for PredMv in decoder
Merge pull request #549 from lyao2/rc_tune

RC LOWBR mode merge
Merge branch 'master' of https://github.com/cisco/openh264 into me_merge6
merge Conflicts:
	codec/encoder/core/inc/svc_motion_estimate.h
	codec/encoder/core/inc/wels_func_ptr_def.h
	codec/encoder/core/src/encoder_ext.cpp
	codec/encoder/core/src/svc_base_layer_md.cpp
	codec/encoder/core/src/svc_motion_estimate.cpp