Allow unregistration of CDI beans at run time, through API

much like the ability to register beans at runtime through API (https://issues.jboss.org/browse/CDI-114)

also provide API

BeanManager::unregister("beanName"), or BeanManager::unregister(XYZBean.class)

to unregister beans at runtime, and corresponding events (BeforeUnregisteringBean, AfterUnregisteringBean, etc) so that interested listeners can take appropriate actions in the event of a bean getting removed from CDI context.

these two together will help build pluggable web applications much like OSGI modules. right now, installing new beans or removing exiting beans requires restart of CDI container, if not web application. with the addition of these two features [registering beans at run time, through BeanManager::register(XYZBean.class) ], and unregistering beans at runtime [BeanManager::unregister(XYZBean.class) ] true modularity comes to Java EE world, without the necessity to restart