Use more human-readable sort order descriptions

Summary:
Anecdotal evidence shows that ascending/descending regularly takes people longer to process than necessary. This patch implements more human-friendly sort order descriptions, in particular:

A-Z/Z-A for text
Newest first/oldest-first for time
Lowest first/highest first for rating
smallest first/largest first for sizes

If there is no string for a particular role defined it will fall back to Ascending/Descending.

I'm aware that not every language uses A-Z. In this case the translator can pick any string that represents the concept of text sorting

Test Plan: Sort view in various ways

Reviewers: Dolphin, VDG, ngraham

Reviewed By: Dolphin, VDG, ngraham

Subscribers: ngraham, kfm-devel

Tags: Dolphin

Differential Revision: https://phabricator.kde.org/D22006