ratecontrol: bug fix - qp for ABR cant exceed MAX_QP  = 51
ratecontrol: remove redundant clip and double conversions
ratecontrol: avoid some operations in CQP mode

--HG--
extra : amend_source : ed1c4e0b410e7accf53f52f163fcf2b98e27f13f
ratecontrol: avoid lookahead overhead for CQP
dpb: we don't need to pass the FrameEncoder to DPB::prepareEncode()
frameencoder: move lambda initialization into the frame worker thread
frameencoder: nits
frameencoder: improve comments
frameencoder: inline resetEncoder
frameencoder: remove unused accessor methods
frameencoder: remove unused accessor methods, inline scaling list sets
frameencoder: remove broadcast methods, inline row initializations