Added right click menu to preview plugin and reorganized code. Also fixed regression regarding thumbnail size and added gtk pixbuf thumbnail generation if pillow isn't available.

Dont print stanzas of received duplicates to the log

https://xmpp.org/extensions/inbox/eme.html

A Body is added with an info message, if there is
a resource online that doesnt support OMEMO

Commit 9d7306001 introduced a syntax error by including a line break in the
description.

this package doesnt play well with demandimport
it hast to be importet at start