We thank all of our co-workers, whose names appear in the related references, for their significant contributions to this review. This work was supported by the National Key Research and Development Program of China (Grant 2016YFA0203002), National Natural Science Funds for Distinguished Young Scholars (Grant 21425728), the National Basic Research Program of China (973 Program) (Grant 2013CB632402), the National Science Foundation of China (Grant 51472100), and an Excellent Doctoral Dissertation Cultivation Grant from the Central China Normal University (Grant 2015YBZD018 and 2016YBZZ034).