SEC-2119: Add a 'form-parameter' attribute to <remember-me>

This change extends the namespace configuration of <remember-me>
with a 'form-parameter' attribute. The introduced attribute sets
the 'parameter' property of  AbstractRememberMeServices.

This enables overriding the default value of
'_spring_security_remember_me' using the namespace configuration.
SEC-2119: Polish remember-me@rememberme-parameter

  - Change form-parameter to rememerme-parameter
  - Use rnc file for generating the xsd
  - Add test for deafult value of rememberme parameter