arbitrary user attributes - Arnold for Katana

KtoA looks for geometry.arbitrary.<attrname> attribute groups following the Katana specification. It adds one special child attribute to specify special Arnold parameter types:

• geometry.arbitrary.<attrname>.arnoldOutputType: a string attribute indicating the destination type of the Arnold parameter.  If not used, this attribute should be left unset, or it should be set to the same type as geometry.arbitrary.<attrname>.outputType.  The only special Arnold types are "node" and "pointer", and in that case, both geometry.arbitrary.<attrname>.inputType and geometry.arbitrary.<attrname>.outputType should be set to "string".  The value(s) should be location paths.