Bug 18298: Use the validate jQuery plugin

Bug 18298: Use the validate jQuery plugin

To validate password fields we need to use the validate jQuery plugin.
To make things reusable this patch adds a new include file
'password_check.inc' at the intranet and opac sides, it creates 3 new
validation methods:
- password_strong => make sure the passwords are strong enough according
to the values of the RequireStrongPassword and minPasswordLength prefs
- password_no_spaces => prevent passwords to be entered with leading or
trailing spaces
- password_match => make sure both password fields match

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>