added dynamic accessor for const accessors, added result_of::element specializations for same type, change counter bug fix in domain

added dynamic accessor for const accessors
 - specialization for base class base_dynamic_accessor_t and dynamic_accessor_t
 - VTK IO now uses const dynamic accessor
 added result_of::element specializations for same type
 - e.g. result_of::element<VertexType, VertexTypeOrTag>
change counter bug fix in domain
 - change counter pointer was not set in default constructor