Add hyphen between fields and tooltips.

Tooltips tell users what the abbreviated names in the radio button group mean.  The hyphen helps a little in relating the title , which has a hyphen in it, to the two fields.

src/toolbars/SelectionBar.h

@@ -110,6 +110,8 @@ class SelectionBar final : public ToolBar {
    wxStaticText * mLengthTitle;
    wxStaticText * mEndTitle;
 
+   wxStaticText * mHyphen[3];
+
    wxStaticText * mProxy;
    wxStaticText * mStartEndProxy;
    wxStaticText * mStartLengthProxy;