Cache access to mpc-hc.ini (both read and write)
Make access to cached mpc-hc.ini thread-safe

Access to mpc-hc.ini cache map is now serialized.
A race was possible between filter graph thread and main thread, as
some internal filters use CWinApp::GetProfileX() functions to load its
settings.
Save mpc-hc.ini in UTF-8
Merge pull request #48 from alexmarsev/ini_cache

Cache access to the mpc-hc(64).ini for faster settings loading/saving.

Refs: #2837.