Move to the upstream SleekXMPP

- remove the decline command that is not in the trunk (and mediated
  declines are supported nowhere anyway)
- change a bit xhtml-im support
- change the bookmarks management a bit
- Add a verification to avoid crashing when poezio will be launched the
  next time
- Fix the (unrelated) bug when setting a jid affiliation

Signed-off-by: Bertrand Marron <b@pk.am>
Refresh the rooster when canceling the search.

fixes #2195

Signed-off-by: Bertrand Marron <b@pk.am>
Update the installation instructions

Signed-off-by: Bertrand Marron <b@pk.am>
Fix a (hidden) traceback

Do not traceback when we receive a chatstate from someone not in our
rooster.

Signed-off-by: Bertrand Marron <b@pk.am>
Update .gitignore