UI/UX issues with 4.0.1 for Android

The latest update introduced a lot of UX changes and one would wish you didn't force them to people. Here's a rundown of those issues:

1. Password instead of PIN: all Electrum for Android users got used to the PIN, but in the new version, the PIN got converted to a password that uses android keyboard instead of more secure on-screen one. Input methods on Android have a history of being a disguise for spyware.
2. No way to disable password or to prefer PIN over password: if you look at android's lock screen UI/UX, you'll see that it allows the user to set up none or just one primary authentication method (swipe, pattern, PIN, password). Some allow for biometrics, but a more traditional one acts as a backup/fallback. I'd recommend copying this UX
3. Receive tab makes little sense: no QR code, no address, but a lot more friction for the user to share their address and get the money

Please, consider rolling these changes back

No files or tests are named. Compare Android 4.0.1 with the previous behavior, then trace the PIN/password flow and the Receive tab entry point. Done means addressing the requested authentication choices and restoring an easy way to display and share a receiving address, with the relevant Android behavior checked.