Created sbt build for DFDL schema. Can use sbt to create and publish a
jar containing a DFDL schema, and then use it on the classpath from
daffodil.
Changes based on IBMers review of latest version. Some required
properties were not declared, expressions were using "=" not "eq", and
there was use of lengthUnits 'bits' for xs:nonNegativeInteger, which is
not allowed.

The latter was fixed by making the opaque future-use group objects into
an array of unsignedInt of length 32, followed by a single unsigned int
containing from 1 to 31 bits.