Stop storing default settings in local storage

Problem/Motivation

This point was first raised in ✨ Allow setting defaults for preview display settings Active . Preview settings are always stored in local storage after opening the preview pane for the first time, even if the user didn't actually change any settings. This makes it hard to change site-wide defaults.

Proposed resolution

Only store settings in local storage once the users actually changes them. Until then, read the default, site-wide settings.