Don't try to use similar code as for OS X to manage windows, events
etc. I.e. don't use UIKit in vcl to do that. Instead, just do as in
the Android port, use the "headless" vcl backend. Do keep using
CoreText, though, not FreeType & fontconfig.

Start changing the iOS "Viewer" app to correspond to the Android
"desktop" app (so it should be renamed).

Work in progress since a long time, several crucial details still
missing, but committing for now.

Change-Id: Iac5fbf8def415e4d0d21e5200450a373420ad7ee