Df input

Implementation of factory class template and its integration in AbstractRecord::factory method
Demonstration in unit tests and in FieldAlgoBase<>.
Make macro in factory.h to simplify these declarations:
FLOW123D_REGISTRAR_DEF( class, name, args)
class = FieldConstant<spacedim,Value>
name="FieldConstatnt"
args = unsigned int (this should be variadic macro parameter)