Tweaks for the PG problem editor for course info files.

This wraps the injected course info html in a `div` that has overflow
auto set.  If the course info file has long contents, then those
contents currently extend past the containing div, and this fixes that.

In addition padding and a background color are added to improve the
appearance.  These are the same styles that are used when this is
displayed in the actual info box.

htdocs/js/PGProblemEditor/pgproblemeditor.js

@@ -303,7 +303,7 @@
 
 		if (fileType === 'course_info') {
 			const contents = webworkConfig?.pgCodeMirror?.getValue();
-			if (contents) renderArea.innerHTML = contents;
+			if (contents) renderArea.innerHTML = `<div class="overflow-auto p-2 bg-light">${contents}</div>`;
 			else
 				renderArea.innerHTML = '<div class="alert alert-danger p-1 m-2 fw-bold">The file has no content.</div>';