Basic setup: merge Group and Register Phone tabs

[mjs]

It's confusing having the group selection and registration functionality on different tabs given that these are part of the same process. It's even more confusing if the setup wizard is used once the device is already registered. It would be clearer if there was just a single tab for registration.

Use a drop down (a "Spinner" in Android parlance) to allow the user to select an existing group. Make the first time in the list should be "New..." which if selected let's the user enter their own group name. See https://developer.android.com/guide/topics/ui/controls/spinner.html.

If the device is already registered, this tab should show the group and device name as text labels (not in form input fields as is done now) and have a "Un-register" button (already done).

[timhot]

Menno: I'd like to assign this to Tom Varley [email protected] but he isn't in the list of assignees.

Tim

[mjs]

I've just invited @tvarleydev to the Contributors group. When he accepts the invite you should be able to assign issues here to him.