Add support for DDL generation from the annotated entity beans ... and optionally executing the generated scripts.

Note that this involves a major refactor of the internals to remove the dependency on the DB meta data that Ebean *has* used (to find/define foreign key relationships etc.

Note as part of this the Insert/Update/Delete functionality of MapBean's has been removed. MapBean is now replaced by SqlRow which is renamed and had the EntityBean interface support removed.