Policy Plus - Highlighted category information

Yesterday, I noticed that categories can have explanation texts too, so I adjusted the ADMX loading system to read them. Today, I changed the Policy Plus main form to display information about categories when they're highlighted in the listing of another category. The category name, description, and count of contents are displayed.

The "App runtime" category selected

In the process, I introduced (and published, whoops) a bug that caused a crash when highlighting a category without an explanation. VB.NET partially - but not completely - smooths over the difference between blank strings and null strings. Before publishing, I had changed the explanation trimming logic into a call to the instance String.Trim method, but that's a null reference exception if the string is null. I fixed it by having AdmxBundle.ResolveString return blank strings when given null strings.

There are only two more Hard Problems to solve that I can see: figuring out the state of all the extra options for policies, and saving changes to policies. I'll start on the former next.