Add setHtmlMessage methods

Hi David,

In SimpleDialogFragment I changed the type of mMessage from String to CharSequence.

This is because Html.fromHtml(String) returns a Spanned, and not a String. Both Spanned and String implement CharSequence, so I think it works the way I wrote it this time.

Sorry it took some time to write this minor patch. It is my first contribution to OSS project, so I had to learn how to do some things in git.

Best,
  Frank