Annotates columns.

@param columnConfiguration
@returns {function(Function)}
@constructor
function Column(columnConfiguration) {
    return function (targetObject, propertyKey) {
        var entityMetadata = targetObject;
        if (!entityMetadata.columnMap) {
            entityMetadata.columnMap = {};
        }
        entityMetadata.columnMap[propertyKey] = columnConfiguration;
    };
}