(bug 65758) WbQuantity may represent various value types

- we get a string from Wikibase; evaluate it to the right
  number type.
- closing braket for WbQuantity.__repr__() string
- test suite added

Change-Id: I4dbc8a267fa37ba613001b8dfeb64458e2e287fe
Merge "(bug 65758) WbQuantity may represent various value types"