(thanks eijebong)

e.g. /set . notify_messages false would set the option for a section
named after the current tab.

(the command args parser would never parse three args, making /set
unable to set section-specific options)

/set displays its results in the form “option=value”, so allowing the
command to interpret the same format as a valid command is only logical
(and allows quick copy/paste and edit).

now we can edit stuff, save or cancel those modifications, and change
the chose storage easily

move the modulename to bookmark → boookmarks
add a bookmarklist class with
remove module-level variables
do a features check on startup before trying to fetch
    the bookmarks

Also add /filter_from and /filter_to, and allow chaining filters.

Avoid surprises with some commands accepting quoted arguments and some other
not.

fix #2555

Should work for any case (plugin, different section, etc)

Make the "default" parameter optional and thus move it to the end of
the command with the other optional parameters.

And change all the calls.

The /reconnect command should now properly work everytime.

(keep a get_name() fallback just in case for now)

- destroy the current room if no parameter
- destroy the room given as a parameter if any
- no reason or alt room because it would be ambiguous in a command
  (implementation ideas welcome)