Custom scheme for levels tech

[blond]

Use scanner function for custom scheme of level:

nodeConfig.addTech([require('enb-bem/techs/levels'), { 
    levels: getLevels(config) 
}]);

function getLevels(config) {
    return [{
        path: 'common.blocks',
        scanner: function () {/*...*/}
    }].map(function (level) { 
        return config.resolvePath(level);
    });
}