Simplify templates to use qrc:/ instead of qrc:///

Both forms are functionally equivalent, but the official documentation
favors the shorter one.

Change-Id: I2b6fccfafc2474f5b61ed6dce460b0472a63854c
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>
Reviewed-by: Alessandro Portale <alessandro.portale@digia.com>