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.
In the discussion in #365, we were imagining that the dialog fragment would call the method directly as in the [link I previously posted](http://developer.android.com/training/basics/fragments/communicating.html)...  But this is fine for now, we can change to the new scheme once we implement the rest of the `DialogFragment`s