Fixes getUniform() method return values and types.

getUniform() method now returns correct types according
to the WebGL specification. Also number of returned values
was fixed.

Change-Id: I71d82ce09af462ddc420e1fd8be1cd5d96a4122d
Reviewed-by: Tomi Korpipää <tomi.korpipaa@theqtcompany.com>
Reviewed-by: Pasi Keränen <pasi.keranen@digia.com>
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@theqtcompany.com>