Annotates columns.

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