Merge pull request #7 from wagh/devel

Devel
host ring table entries MonomialMatrix

(outsourced from GradedRingForHomalg v2013.07.14)

(needs MatricesForHomalg, HomalgToCAS v2013.07.14)
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