Triggering logoutUrl navigation after calling signOut API in the client.

bigbluebutton-client/src/org/bigbluebutton/core/BBB.as

.../src/org/bigbluebutton/core/managers/UserConfigManager.as

...ent/src/org/bigbluebutton/main/views/LoggedOutWindow.mxml

...rs/org/bigbluebutton/web/controllers/ApiController.groovy