WSDL should be read once

see http://anonsvn.jboss.org/repos/jbosstools/trunk/ws/plugins/org.jboss.tools.ws.creation.core/src/org/jboss/tools/ws/creation/core/commands/ImplementationClassCreationCommand.java

The class is involved in Top-Down web service scenario where it is responsible for creating a web service implementation class from artifacts generated by wscosume tool and user supplied WSDL. The problem with this class is that for each data it needs to know from wsdl there is separate read from external resource (local WSDL file) - see getTNSFromWSDL(), getServiceNameFromWSDL() (as of r27544) and this can cause some performance penalty in case of big WSDL. The code should be changed so the particular WSDL is read only once per wizard's run.