Add vimb and weechat to dotfiles (externally tracked)

Externally stored because:

 *  vimb config could be a bit security-sensitive thing, at least until
    I find out what I want in there and how to split things properly.

 *  Same appliest to weechat, plus it has this habit of rewriting config
    on exit, which could become annoying if stored in git and changed
    frequently.

dotfiles.config/vimb

+../external/dotfiles.config/vimb

dotfiles/weechat

+../../../st/config/dotfiles/weechat