Enhance measurement system support in routing manager.

It is useful to be able to set the measurement system independently of
the locale used by the routing manager. Add accessor functions for the
measurement system to the routing manager classes.

Locale and measurement system properties are also added to the
RouteModel QML type.

Change-Id: I8ee9fbdb5ab94615fef7019914b0f104aebfa9c8
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>