Add command icons

[leoapagano]

This is an issue that's been bugging me for a long time that turned out to be super easy to fix. Previously, when adding the Underline and Center commands to the mobile toolbars, it just shows a "?". Now, these two commands, as well as the other two "Link to heading" and "Link to block" commands, all have command icons. No extra files are needed for this - it uses Obsidian's built-in Lucide icons.

Before...

vs after...