Fix RFC 6122 implementation

JID resourceparts should be able to contain "@" and "/" characters
"example.net/@/" should be a valid JID.

Retab JID file
Allow JIDs such as "example.net/@"
Update/improve German translations
cleaned up avatar / tile creation
fixed potential npes in message parser
clean up getProposedNick
safety net in joinMuc
Merge branch 'development' of https://github.com/siacs/Conversations into development
Merge pull request #743 from weiss/update-german-translations

Update/improve German translations
Merge pull request #740 from SamWhited/jidrpfix

Fix RFC 6122 implementation