picsym: remove trivial access methods, cleanup

Remove redundant data, use intptr_t more consistently for picture strides.
Yuv stride can stay as int, the strides are never more than 64 bytes. Use
uint32_t for block counters

Rename getCU() as getPicCTU() for clarity
pull TComPicSym into common/ as FrameData

Document the nature in how these are reused by multiple pictures.
Frame::m_picSym was renamed to Frame::m_encData to make the relationship more
clear.
cmake: quiet -Wmaybe-uninitialized warnings in encoder/

gcc >= 4.8 is catching false positives from Clip3 (std::min<>(std::max<>)) when
the arguments are all known at compile time.  Just shut-up, please.
cmake: newer GCC/MinGW define __rdtsc and do not like our redefinition