Integrate and test an interface for the Lurch plugin

Epic: https://source.puri.sm/Librem5/use-cases/issues/50

The Lurch plugin maintainer has worked on an API to integrate with Chatty. The Chatty UI needs to be enhanced for making the new plugin functions available. This plugin is essential to having E2EE XMPP.

Testing the interface
A couple of issues in the Lurch API need to be fixed
Preparing the UI for showing OMEMO fingerprints
Preparing the UI for switching OMEMO on/off in conversations
Binding the Lurch API functions
Testing the API

Edited Jul 02, 2019 by Andrea Schaefer

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