MIRA: Move selection dialog to dialog package
The RelatedRequirmentsSelectDialog, RelatedRequirmentsSelectDialogGUI is
similar to ElementTreeMultiSelectEditableDialog, …GUI.
Therefore, the dialog should be renamed consistently, eventually
refactored and the basic dialog should be extracted to
org.fortiss.af3.mira.ui.dialog.
(from redmine: issue id 2024, created on 2014-06-16, closed on 2014-10-15)