Fix a bug in the status plugin

(if python had real closures, I would not need that)
Fix #2182 (show s2s errors)

- Add the theming options COLOR_ROSTER_ERROR, CHAR_ROSTER_ERRROR, and
    CHAR_ROSTER_ASKED
Fix #1923 (caps)
Update CHANGELOG with a bunch of commits
Fix a typo in the documentation
Fix #2126 (per-server configuration sections)

(also move replace_key_with_bound() to core.py, to prevent having
common.py depending of config.py)