Command Line refactoring

[RunDevelopment]

This fixes #2289.

The actual fix is quite simple:

-if (env.element.querySelector('.command-line-prompt')) { // Abort if prompt already exists.
-	commandLine.complete = true;
-	return;
-}
+// The element might be highlighted multiple times, so we just remove the previous prompt
+var existingPrompt = env.element.querySelector('.command-line-prompt');
+if (existingPrompt) {
+	existingPrompt.remove();
+}

But I also took the time to refactor Command Line a little.

[mAAdhaTTah]

It would be easier to review this if the stylistic changes were in a separate PR. Between the refactor, the actual change, & the indentation, I'm not really sure what I'm looking at here.

[mAAdhaTTah]

This was easier to review once I turned whitespace changes off. This looks good.