Extend smw.dataItem and smw.dataItem.factory()

+ smw.dataItem.unknown be used for all types that are not recognized as
"official" dataitems
+ smw.dataItem.number
+ smw.dataItem.text (represents text and string values)
+ smw.dataValue.quantity

## QUnit
+ Adopted ext.smw.dataItem.factory test
+ Add ext.smw.dataItem.unknown.test
+ Add ext.smw.dataItem.text.test
+ Add ext.smw.dataItem.number.test
+ Add ext.smw.dataValue.quantity.text

Change-Id: I67bd14327a953fe3309e5645ac17d2bc0a736664