Made repository fetch/create static functions.

Made QubitFlatfileImport repository fetch/create functions static so they
can be used as helpers.
Added MODS bulk import.

Added MODS import convertor (and support for MODS import in
QubitXmlImport class).
Added material type conversion to MODS export.

Added automatic conversion of RAD GMD to MODS resource
types in MODS export.