Implement UIAlertController for Android

[ephemer]

We want to be able to show Alerts e.g. for MIDI device connected, something isn't working as expected etc.

[michaelknoch]

should we implement this in an iOS or android look and feel?

[ephemer]

Note that we're entering the realm of Android UX expectations with this task. We should implement this to look and feel like Android, and not like iOS.

I would also explicitly implement it as an Android component, i.e.:

open class AndroidUIAlertController {
  // implementation
}

in another file (UIAlertController.swift):

// Later we can add #if os(Android) etc. here, but for now we can use the Android version everywhere
public typealias UIAlertController = AndroidUIAlertController