Add comment about the need to set the keyframe flag.
Remove keyframe flag correction code because it apparently makes things worse (for MP4+H.264).
Add translations for message box buttons.
Merge branch 'master' into backported-translation

Conflicts:
	src/translations/simplescreenrecorder_de.ts
	src/translations/simplescreenrecorder_nl.ts
	src/translations/simplescreenrecorder_pl.ts
	src/translations/simplescreenrecorder_zh_CN.ts
Update translations.