Data is lost in JSON String deserialization

Clippings is lost when deserializing JSON Strings

See test at
https://github.com/ecologylab/BigSemanticsJava/blob/dev/BigSemanticsSDK/test/ecologylab/bigsemantics/metadata/DeserializationTest.java

Deserialization of XML produces the warning

WARNING - class ecologylab.bigsemantics.metadata.MetadataDeserializationHookStrategy:  polymorphicly looking up meta-metadata failed: cannot find mmd named as clippings