Fix Memory leak in CDI plugin

The CDI plugin was using a single 'CreationalContext' for all beans created by the CDIObjectFactory. This is incorrect and the size of the 'dependentInstances' (in the WELD implementation) grows indefinately with no beans being removed. 
Fix is to use a new 'CreationalContext' for every bean created. In our tests with WELD this does not effect the applications performance. Idealy a single 'CreationalContext' should be created for the request lifecycle. However the struts ObjectFactory API does not appear to provide any information able the lifecycle.