Doc: Added a QML module page for Qt Quick Test

This should avoid the TestCase and SignalSpy
types being listed in the All Classes page, which
is meant for the C++ classes.

Task-number: QTBUG-33316
Change-Id: I0f2f9e557df89f46f656a8820602fe5712c64073
Reviewed-by: Caroline Chao <caroline.chao@digia.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>