Allow http session listeners to be injected as a spring bean

If a module needs to be notified of http session events, it currently forces the end project to register it's listener in the web.xml. If it were possible to do this via spring, additional modules could be added to a project without the need for such changes.

A generic HST http session listener should be sufficient; it can dispatch a generic http session event to the application context. If those events are propagated to all the module app contexts automatically, the wiriing is minimal.