JVET-X0079: Add new level 6.3
Adds level 6.3 as adopted in JVET-X0079 g_uiMaxCpbSize is re-indexed as adding 6.3 increases maximum number of sub-levels from 3 to 4.
Adds level 6.3 as adopted in JVET-X0079 g_uiMaxCpbSize is re-indexed as adding 6.3 increases maximum number of sub-levels from 3 to 4.