Package CDI support as a separate module

I'd like to suggest removing the CDI support from liquibase-core and packaging it as a separate module.  The CDI code seems to work only with JBoss Weld and is effectively a poison-pill when deployed in an OpenEJB environment.  It might be worth packaging all the flavors of integration separately.

I have a fork, with a new liquibase-cdi module, that's working well for me.  I'll try to keep it up to date.  Please consider making this change.  As it is, the CDI code is a show-stopper.

djh