Add natural sorting and case-insensitive sorting for all role-types

Summary:
Add natural sorting and case-insensitive sorting, for all role-types
that benefit from.

BUG: 406296
FIXED-IN: 19.12.2

Test Plan:
Sort by any role type specified in isRoleValueNatural()
Before: Sorting is always case sensitive
After: Sorting according to 'Sorting mode' in configuration.

Reviewers: Dolphin, nicolasfella, meven, elvisangelaccio, ngraham

Reviewed By: Dolphin, meven, elvisangelaccio, ngraham

Subscribers: cfeck, meven, kfm-devel

Tags: Dolphin

Differential Revision: https://phabricator.kde.org/D25741