Reintroduce KCoreDirLister::setMimeExcludeFilter
This was marked as deprecated and removed in !1129 (merged) for lack of known users.
Dolphin could become a user to fix bug 3212.
Partial revert of 8e452cde
This was marked as deprecated and removed in !1129 (merged) for lack of known users.
Dolphin could become a user to fix bug 3212.
Partial revert of 8e452cde