#2 Improve user account administration

[texas_stu]

Currently XMLTester user accounts are controlled via
an htpasswd style file
(security/xmltester_demo_realm.properties). To add an
account, this file
must be edited and the XMLTester server must
be restarted. It should be possible to add a user
account, change the password, etc. without restarting
the XMLTester server.