merge TComBitCounter into TComBitStream.h
always include CommonDef.h via common.h, avoid include loops

Remove some spurious stdlib includes not in common.h
TComSlice: remove layer violation include

files in common/ shouldn't include encoder/ headers
bitstream: simplify TComBitStream interface and code
nal: add back comments now that member variables are gone
bitstream: fast-path for appending bitstreams