ui/app: make Draw.Config a value, not a pointer

We are going to encourage a model where pointers to a central
(program global) Configs are passed to widgets at setup time, and
not pass Configs at every frame.

That way, the global Gonfig can change, but the pointers won't need
updating.

This change only switches the Draw event's Config pointer to a value
to avoid tempting programs to use the event Config instead of
updating their own central Configs.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/app/os_android.go

@@ -275,7 +275,7 @@ func (w *window) draw(sync bool) {
 			X: int(width),
 			Y: int(height),
 		},
-		Config: &ui.Config{
+		Config: ui.Config{
 			PxPerDp: ppdp,
 			PxPerSp: w.fontScale * ppdp,
 			Now:     time.Now(),