addPreProcessor(preProcessor, priority) {
        let indexToInsertAt;
        for (indexToInsertAt = 0; indexToInsertAt < this.preProcessors.length; indexToInsertAt++) {
            if (this.preProcessors[indexToInsertAt].priority >= priority) {
                break;
            }
        }
        this.preProcessors.splice(indexToInsertAt, 0, {preProcessor, priority});
    }
Adds a pre processor object
@param {object} preProcessor
@param {number} priority - guidelines 1 = before import, 1000 = import, 2000 = after import