Don't allow selecting the same recipient more than once

[Luke Klinker]

Note: Copied from https://github.com/klinker-apps/messenger-issues/issues/689

Device with issue: Samsung Galaxy A7 (2017)
App version: 3.1.1.2131
Steps to reproduce:

1. Click on fab
2. Choose the same recepeint for a few times

Additional information:

Possible solution:

Just avoid duplicating items by removing a chosen recipient from the list after adding him to the edit box.