Hide Guacamole Connection Settings menu button when not authorized

[jochenwezel]

Current situation

• The Guacamole Connection Settings page is only available for admin users at Guacamole.
• The menu button for Guacamole Connection Settings is clicked, but the non-admin-user gets redirected to connection home => confusing for user / unexpected behaviour

Requirement

• Track logon status
  • if logged on, test once for connections page authorization status by checking http status response of Guacamole Connection Settings page url
    • status code 200 or redirect to {serverurl}/#/settings/preferences with a status code 200 there => user is admin, show menu button
    • status code 404 or redirect to connection home or {connection home}/#/ with status code 200 => user is unprivileged user, hide menu button
  • if login form appears, user is logged out => button is already hidden by existing logic, but we must reset cached connections page authorization status
• Test connections page authorization status in background as soon as user is logged on

Considerations

• code for page/url checks already exists in GuacamoleCommon project in class GuacamoleUrlAndContentChecks
• further tests might extend existing class GuacamoleUrlAndContentChecks