Enable recursive filtering in EntityOrderProxyModel
Summary: This allows to use it for the folder tree lineedit in kmail.
Test Plan:
No-op in itself (this proxy is currently only used for ordering),
but this commit allows mailcommon's foldertreewidget to use this proxy
for filtering, instead of filtering FolderTreeWidgetProxyModel
(which is shared with the favorites model, where we don't want filtering)
BIC of course, but I was told that's OK.
Reviewers: dvratil
Reviewed By: dvratil
Subscribers: KDE PIM
Tags: KDE PIM
Differential Revision: https://phabricator.kde.org/D8799