Make Qt 5.2 a minimum requirement

Cleanup version ifdefs and v8-private dependencies.

Change-Id: Iac393c06dfba02499e60d713d9f4d04ef0c9e617
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Fixup QtQuick autotests with scene graph usage

Change-Id: Ib49ac987af9fd6af32708048613fc5e6442bb73f
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>
Reviewed-by: Andras Becsi <andras.becsi@digia.com>