Allow custom icons & no icon

[SoCuul]

It would be great to be able to add custom icons (from either png/svg) as well as setting a blank icon (currently you have to manually edit the db.json file to set an invalid icon id)

[antonreshetov]

You can simply press the "Reset" button to return to the default icon.

[SoCuul]

Unfortunately I'm not talking about the default icon, but an "icon" that has no texture. Basically a fully transparent icon, that looks like there's no icon there.