added CopyElement ring table entries to Singular and MAGMA

i.e., to
. CommonHomalgTableForSingularTools
. CommonHomalgTableForMAGMATools

(supports the new method \/ in HomalgToCAS v2013.07.15)
Replace HomalgRingElement by HomalgExternalRingElement
Merge pull request #8 from wagh/devel

Replace HomalgRingElement by HomalgExternalRingElement