frontends: small message refactorisation: - factorize some treatments that were done both in Primitivus and Libervia - the way it was done, especially with QuickChat.printMessage returning a tuple, was quite disturbing - FIXME: we can probably remove some arguments and do a deeper factorization e.g with QuickChatText

Use this module to temporary store files that need to be integrated to other
projects such as Wokkel.

For example, the changeset that introduced this folder adds RSM (XEP-0059)
support to Wokkel. The files in sat.tmp.wokkel are imported over the initial
wokkel files from sat.plugins.__init__.py