Formatting fixes, consistency with GUI
Summary: Wider usage of :guilabel:, :kbd: and |mouse...|, fix typos, headers (remove colons and periods), sync some items with GUI.
Test Plan: none
Reviewers: Krita, Krita: Manual, woltherav
Reviewed By: Krita, Krita: Manual, woltherav
Tags: Krita: Manual
Differential Revision: https://phabricator.kde.org/D19574