Blacklist Accusoft PICVideo M-JPEG Codec 2.1 since causes some crashes.

Newer versions of the decoder have a different CLSID and don't crash.
Graph builder: improve debug output.
Fix: The external filters list was lost when switching from registry to ini or vice-versa.
Cosmetics: Use directly m_s instead of AfxGetAppSettings() when possible.
PPageSubMisc: cosmetics.

* Use more meaningful functions names.
* Use correct visibility for the members variables and functions.
Fixed DXVA1 MPEG2 decoding.

This commit fixes #2913.
Cosmetics: add missing brackets and consistently use .0f instead of .f.
Mpeg2DecFilter.cpp: fix a useless dereference
Initialize variables in the constructor.
Cppcheck fixes:

* reduce variable scope
* remove unneeded variable assignments