PCA: Ensure mean centered table is output + other fixes

Pivotal: 54329628

[Changes applicable to PCA Train and PCA Project]
1. PCA Training - New output table will be created during PCA training.
    - outputtable_mean. This table is the mean of the input data
    matrix.
2. PCA project - will use this output (mean of the training set) for
    projecting to the test table.
3. PCA project - accepts col-format input data matrix
    (like SVD and PCA_train).
4. Both - Added user documentation to explain how this is
    being done.
5. Changed computation of Eigen values in PCA to divide by sqrt(n-1)