Switch Lists to Sets for avoiding duplicates.

This commit also automatically marks inputType for EmailAutoCompleteTextView as email. This displays a friendlier keyboard layout in case the user's email isn't on the device.

Also added `android:actionLabel` in the README for folks who might find it helpful.

Tips from https://plus.google.com/110199935346260350060/posts/CNkNa5N6rMz
Merge pull request #3 from f2prateek/f2prateek/sets

Switch Lists to Sets for avoiding duplicates. UX Tweaks.