Add a Dialog an ExApp page can open for a message, confirm, or prompt.

The page waits for the choice. App navigation includes the same piece.

navigation.go

@@ -105,6 +105,7 @@ func (n AppNavigation) serve(w http.ResponseWriter, r *http.Request) {
 		Missing:  msg,
 		Title:    title,
 		Theme:    !n.DisableTheme,
+		Dialog:   DialogHTML(),
 	})
 }
 
@@ -135,6 +136,7 @@ type shellView struct {
 	Missing  string
 	Title    string
 	Theme    bool
+	Dialog   template.HTML
 }
 
 type itemView struct {
@@ -295,6 +297,7 @@ var shellTmpl = template.Must(template.New("shell").Parse(`<!DOCTYPE html>
 </style>
 </head>
 <body data-selected="{{.Selected}}" data-address="{{.Address}}">
+{{.Dialog}}
 <div id="app-nav">
   <div id="nav-header">{{.Header}}</div>
   <div id="app-nav-body">