Various ThreadLocal memory leaks

There are a number of ThreadLocals in PicoContainer and PWR that are not correctly disposed of.

DefaultPicoContainer#dispose should call

intoThreadLocal.remove();
intoThreadLocal = null;

DefaultPicoContainer#getComponent(Object, Type) should call

        } finally {
            intoThreadLocal.set(null);
            intoThreadLocal.remove();
        }

PicoServletContainerListener#contextDestroyed doesn't remove the ScopedContainers instance from the servlet context:

    public void contextDestroyed(ServletContextEvent event) {
        ScopedContainers scopedContainers = getScopedContainers(event.getServletContext());
        stop(scopedContainers.getApplicationContainer());
        dispose(scopedContainers.getApplicationContainer());
    }

Storing#mapThreadLocalObjectReference should not be final and should be nulled by PicoServletContainerListener#contextDestroyed.

I think that should help with the errors logged by Tomcat.