API2 Rework: sws rescaler

Adopt VideoRescaler to work with VideoFrame2
API2 Rework: new method isFlags() in Format<T> class

Method checks that provided flags is set return true on success, false
otherwise.
API2 Rework: fix possible corrupt in CodecContext::isValid()

Check parent stream for valid first, after that check m_raw and m_raw-
still non null, but is free'd, so access to m_raw->codec is invalid.
API2 Rework: Ignore SIGPIPE by default.

Set SIGPIPE signal ignoring in av::init() by default.
API2 Rework: fix/new samples

Fix: api2-samples/av-decode-encode-video.cpp
New: api2-samples/av-scale-video.cpp

Note, av-scale-video.cpp same to av-decode-encode-video.cpp but contain
scaler. Scaler setted automaticaly on demaind.