Support device verification

**Is your feature request related to a problem? Please describe.**
Yes i know it is written in FAQ, that it is not implemented yes.
It does not mean, that this should be implemented in future, herefore this Issue.

To response verification to other devices (from other accounts) is necessary to trust the conversation in a room.

**Describe the solution you'd like**
I like Emojis

**Describe alternatives you've considered**
QR-Codes are also fine