[FIX] web,mail: widgets: replace $el.toggle() by do_toggle()

Since rev. 16eb36ff, do_show() and do_hide() on widgets toggle the classname
o_hidden on which the rule 'display: none' is defined, instead of calling
jQuery's show() and hide().

The method do_toggle(), sharing the same logic, has been introduced in rev.
74c5f772.

From now on, every widgets should call do_toggle() instead of $el.toggle() as
it will have undesiderable effects (they should call do_show() and do_hide()
instead of $el.show() and $el.hide() as well, this as been done in 16eb36ff).

This rev. replaces all calls to $el.toggle() by do_toggle(). It also adds
an optional argument to do_toggle() to force hidding or showing the widget.