SMW\DISerializer export formatting relevant info

Make getOutputFormat() available and enable printRequest related
formatting to be exported.

* Support printrequests that can carry an additional notion such as Modification date#ISO (see [1] ).

* Fixed [{\"value\":188,\"unit\":\"km\\u00b2\"},777.00077700078] turns into
[{\"value\":188,\"unit\":\"km\\u00b2\"},{\"value\":777.00077700078,\"unit\":\"km\\u00b2\"}],
when another quantity was part of the same $resultArray array_map would
invoke an empty $printRequest array (which normally contains the _qty type
indentification) showing a number instead of a quantity

[1] http://www.semantic-mediawiki.org/wiki/Help:Displaying_information#Formats_for_specific_printout_types

Change-Id: I44a563d28f5f61b36ef384ba3a377e5442fd7e3c