Supporting init and destroy callback options

This spawns a few questions:
1) Should this be in WebComponent instead?
2) These mirror the methods in the Servlet interface, but I'm not sure
they're called at the same relative times as Undertow would for actual
Servlets. Specifically, the Servlet spec says they're called *before*
the servlet is about to either by initialized or destroyed, but in
Immutant, we do it *after*.
3) Does Ruby/Rack support these guys?