[WIP] Incremental PCA

Work in progress for Incremental PCA. It seems pretty close, but the SVD is still flipping around dimensions. Adding ```svd_flip``` seems not to help. Currently, the computation is on columns, because the original paper is done this way, and converting to row based was very difficult. See [Incremental Learning for Visual Tracking, J. Lim, D. Ross, R. Lin, M. Yang, 2004](http://www.cs.toronto.edu/~dross/ivt/LimRossLinYang_nips04.pdf) for more details.