new common types for group elements

Definition of new common types for general group elements.

Should be used in signalGroup, baliseGroup and trainGroup.

This new type is designed as "extension base type" for these elements.

New common type tGroupElement

• extended based on tElementWithIdAndName, provides attributes id, name, description, anyAttribute

• with child element member of tElementWithSequence

New common type tElementWithSequence

• extended based on tElementWithReference, provides attribute ref

• with attribute sequence of tCounter