remove Props.get and simplify DDWriter and Attribute2PartialEntityWriter implicits

we have no need to write data to anything more specific than DatomicData
Props is a heterogenous list but we only need to put things into it, not get them out
remove DInt and add DDWriter implicits for numeric types

any fixed sized integer type can be upcast to a Long, so we can write any of Byte, Chart, Short, Int, Long, as a DLong