core: replaced SkipHistory exception by a key in mess_data: SkipHistory was skipping all remaining triggers just to skip history, which is not the intented behaviour. Now history can be skipped by setting mess_data[u'history'] = C.HISTORY_SKIP, this way we won't skip importants triggers. When history is skipped, mess_data[u'extra'][u'history'] will be set to C.HISTORY_SKIP for frontends, so they can inform user that the message is not stored locally.

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