ldapadmin - improve the management of password controls

* test equality between passwords even if empty
* also test password strength at "change" event (copy/paste, for example)
* password strength sets red color and "empty" message when password is empty
ldapadmin - 4 spaces for javascript (sorry for the mess)
ldapadmin - do not validate client-side - it must be done server-side

The tests are done client-side at the same time the user is filling the
form. With the previous client-sde validation, the Accept button appeared
to de disabled, because clicking had no effect, even no erreor message.

Important: the validation must be done server-side. This is NOT the case
currently for the password strength check.