- Add a “prepend” attribute to the Line tuple

I’m not sure of the impact of this on performance (we parse the message
yet another time)

(add a new theming option, too)

Also:
- Add get_conversation_messages() to PluginAPI
- Make plugins_autoload colon-separated instead of space-separated
    (for consistency)
- Replace a JID() with a safeJID() in the uptime plugin

- add methods related to timed events to the PluginAPI
- remove parse_command_args_to_alias because str.format does that, and
  better
→ update the alias plugin

(and tell what is failing)

- Try to reduce the use of the “core” object in the plugins
- New “api” member for each BasePlugin which is a wrapper around
    the unique PluginAPI object. (instead of having the methods
    directly in BasePlugin and then calling the PluginManager)
- Documented methods with rst (for sphinx)

(THE NAMESPACE WAS NOT PRESENT ANYMORE)

for consistency

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

- Add the theming options COLOR_ROSTER_ERROR, CHAR_ROSTER_ERRROR, and
    CHAR_ROSTER_ASKED

(if python had real closures, I would not need that)

And fix some imprecisions/mistakes in the help.

fix a TB in the MUC
fix the completion (no quotes)
add a timeout of 5 seconds

- remove the help message for people still using the old custom
    sleekxmpp repo

- reload the config/theme with SIGUSR1
- quit properly with SIGHUP/SIGTERM

- Prevent correction of delayed messages
- Prevent correction of messages by someone else in a MUC (and in a
  private tab)
- Messages with unauthorized corrections (above) or wrong message id
  will be displayed as normal messages

TODO: restrict the corrections to the same fullJID (only in direct
"normal" conversations, because we can know in private an muc tabs, via
the User object)