Show and interpret QR codes for contacts, login, groups and fingerprints

A QR code should be shown for the own JID, a JID of a contact, a JID of a group, login data and OMEMO key fingerprints.

Show and interpret a QR code for a URI containing the following elements:

JID
Example: xmpp:user@example.org

• Show Alice your own QR code so that she can add you.
• Show Alice the QR code of Bob so that she can add him.
• Scan the QR code of Alice to add her.

JID + login action
Example: xmpp:user@example.org?login;password=abc123

• Log in to an account with the given login data.

JID + join action for a group (as soon as MUC is implemented or with a similar action for MIX as soon as that is implemented)
Example: xmpp:discussion@group.example.org?join

• Join a group with the given JID.

JID + fingerprints of an OMEMO identity key Example: xmpp:user@example.org?trust-message;encryption=urn:xmpp:omemo:1;trust=623548d3835c6d33ef5cb680f7944ef381cf712bf23a0119dabe5c4f252cd02f;trust=d9f849b6b828309c5f2c8df4f38fd891887da5aaa24a22c50d52f69b4a80817e

• Authenticate OMEMO identity keys with the given fingerprints.