JPA dependency on org.jboss.as.weld.common should be optional

The org.jboss.as.jpa module depends on org.jboss.as.weld.common in order to load the WeldPortableExtensions class. But this can be optional, as the classloading will only occur if WeldDeploymentMarker.isPartOfWeldDeployment would return 'true' and that will not happen if the weld subsystem is not installed.

This will allow Galleon to not provision that module if it isn't provisioning the weld subsystem.