get deterministic output when frame threading is enabled (for all -Fn, n > 1)

Output mistake reasons:

1. CABAC Table Initialize
   The HM have decide best table for CABAC, but in frame parallelism,
   we can't get this information before thread start, we have to
   disable it now.
Side effect: maybe lost some compress performance

2. SAO Global Disable
   The HM decide SAO global disable flag depend previous same type of
   slice. but here, we can get right statistics informat before start,
   so we have to disable it.
Side effect: more computer cost since we always try SAO on every LCU

3. CABAC status m_frac not reset.
    This HM bug still alive, we found more here.
Enable cli parameters for unidirectional weighted prediction

As part of re-enabling unidirectional weighted prediction after introduction of
frame parallelism
Adding few checks and an init() function in MotionRefrence class

to properly signal malloc failure for 'fpelPlane'; handling to be added later
added states for storing ssim values per frame and globally at encoder level
api: added x265_stats_t structure and x265_encoder_stats() function