Changed to save a Dialog that has at least one dialog field.

- Fixed code to not allow user to save a dialog that does not have at least one dialog field.
- Fixed infinite spinner after an existing resource was removed from a dialog.
- Added controller spec tests for dialog_edit method to verify that dialog is not saved without fields, and another one to verify save of dialog with 1 tab, 2 groups and 1 field.

https://bugzilla.redhat.com/show_bug.cgi?id=1156634
https://bugzilla.redhat.com/show_bug.cgi?id=1157796

@dclarizio please review/test.