Always save view settings when switching from one view mode to another

Summary:

• Add zoom setings for each view kind
• Save and restore zoom when view is changed
• Add default icon size of 64 px for icons view and 32px for compact view

Reviewers: Frameworks, ngraham

Reviewed By: ngraham

Subscribers: kde-frameworks-devel

Tags: Frameworks

Maniphest Tasks: T8552

Differential Revision: https://phabricator.kde.org/D21459