Make it possible to show all spaces in the document

Summary:
It's a feature offered by several editors. Now we allow to render none, only trailing and all of them.

BUG: 381267
BUG: 342811

Test Plan: Tested locally

Reviewers: #kate, cullmann

Reviewed By: #kate, cullmann

Subscribers: cullmann, ngraham, kwrite-devel, kde-frameworks-devel

Tags: #kate, #frameworks

Differential Revision: https://phabricator.kde.org/D19163