"After Playback": Always give "Once" events a higher priority than "Always" events.

This commit fixes #3001.
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
Subtitles: Improve error checking with ASS rendering.

Some crashes could occur when the SSA script was using obviously wrong values.

Uses the same check as libass for maximum glyph size.
Updated German translation.

Thanks to Luan who participated actively to this update.
Updated Czech translation
update Changelog.txt
update docs/Release.txt
German translation: get rid of useless hyphens
Replace "On top > Never" by "On top > Default".

In most of the cases "On top > Default" will have the exact same behavior than "On top > Never" but it won't try to override the "on top" flag if an external tool sets it.

This commit fixes #2689.
Merge pull request #48 from alexmarsev/ini_cache

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