Allow deselecting highlighted operands by clicking on the GUI's background

[LagoLunatic]

When you have an operand highlighted, there are currently two ways to deselect it:

• Click on the operand you already have highlighted, either once (if it's highlighted on both sides) or twice (if it's only highlighted on the side you're clicking on)
• Click on a comma once

It would be convenient if clicking on the background had the same feature as decomp.me where it instantly removes all highlights with one click so you don't have to go hunting for a tiny comma.

Version: 2.2.2