fix issue 1886 and created class TagsDialog

edit: removed old info.

I created a class TagsDialog to handle the tags dialogs. Interesting enough, the problem with the radio buttons doesn't happen anymore. Now they are always red.

Also, the itemlist is now sorted in the TagsDialog class to ensure only tags are sorted. I hope the code is good enough. I've made some tests and I believe it works, but of course, probably needs more testing.