* wl.el (wl-plugged-toggle-all): Set the value of `wl-modeline-plug-status'

* wl.el (wl-plugged-toggle-all): Set the value of `wl-modeline-plug-status'
instead of `wl-plug-state-indicator'.
(wl-plugged-toggle): Ditto.
(wl-toggle-plugged): Ditto.
(wl-plugged-init): Ditto.

* wl-xmas.el (wl-biff-init-icons): Set icons data to
`wl-modeline-biff-state-off' and `wl-modeline-biff-state-on' instead of
`wl-biff-state-indicator-off' and `wl-biff-state-indicator-on';
don't modify the value and the type of `wl-biff-state-indicator-off' and
`wl-biff-state-indicator-on'.
(wl-plugged-init-icons): Set icons data to `wl-modeline-plug-state-off' and
`wl-modeline-plug-state-on' instead of `wl-plug-state-indicator-off' and
`wl-plug-state-indicator-on';
don't modify the value and the type of `wl-plug-state-indicator-off' and
`wl-plug-state-indicator-on'.

* wl-vars.el (wl-modeline-biff-state-off, wl-modeline-biff-state-on,
wl-modeline-biff-status, wl-modeline-plug-state-off, wl-modeline-plug-state-on,
wl-modeline-plug-status): New internal variables.
(wl-biff-state-indicator-off, wl-biff-state-indicator-on,
wl-biff-check-interval, wl-biff-check-folder-list): Change customization group
from `wl-folder' to `wl-highlight'.
(wl-plug-state-indicator-off, wl-plug-state-indicator-on,
wl-show-plug-status-on-modeline): Defcustomized.

* wl-util.el (wl-biff-check-folders): Set the value of the flag
`wl-modeline-biff-status' instead of `wl-biff-state-indicator'.
(wl-mode-line-buffer-identification): Set both ON and OFF data with a flag to
`mode-line-buffer-identification'.

* wl-e21.el (wl-biff-init-icons): Set icons data to
`wl-modeline-biff-state-off' and `wl-modeline-biff-state-on' instead of
`wl-biff-state-indicator-off' and `wl-biff-state-indicator-on'.
(wl-plugged-init-icons): Set icons data to `wl-modeline-plug-state-off' and
`wl-modeline-plug-state-on' instead of `wl-plug-state-indicator-off' and
`wl-plug-state-indicator-on'.