Add extra checks for local storage support

[diamondavocado]

I'm using the UserScript version of the extension in a browser without local storage support.

Although some parts of the code do check for the presence of local storage support in the browser, many parts do not.

This results in the script breaking in browsers with no local storage.

Please consider adding extra checks to handle such situations.

Example Fix

I modified v47 of the user script to include a few more checks for local storage. This makes the comment controls work, at least, which is all I use the extension for.

Here is a comparison before/after the fixes: https://editor.mergely.com/UTLOX9CM