Transform (Offline) ProgressDialog to an Overlay

[Bungeefan]

We should transform the ProgressDialog to an overlay instead of a dialog, as a dialog is very volatile and gets dropped when routing happens. (Which happens in the case of initiating offline)

For example, we could manage it in the JVxOverlay similar to the "Connected" overlay.

[rjahn]

I guess this is not a problem because routing happens in any case and dialog should be closed after routing?

[Bungeefan]

We still have some steps to take after we close the screen, therefore, it should probably be possible to show these and not rely on them always being fast and never failing.

[rjahn]

Please add test details and what should happen!

[Bungeefan]

The idea was that a managed overlay, like the already existing "overlays" in JVxOverlay, would be infinitely better than the volatile dialog.

Dialogs are bound to the currently active navigator which in turn is "bound" to the current route, therefore, every dialog will be "closed" (popped) when the navigator receives a route request from the managing router.
Technically, it would be possible to just recreate the dialog after the routing, but this would just move the problem and probably create new ones.

The "problem" that this was aiming to solve, is that there are still tasks to be completed after the routing, but in case they take longer or failed, there is no user indication.