Fitting PCA on AbstractArrays

[oxinabox]

It would be good if PCA supported any type of array that support the required methods.
and sored what ever projection matrix those methods came up with.

For example:
NamedDims.jl supports svd and will give you a partially named projection matrix.
Which can be pretty useful; since it will enforce and propagate it's names/
But if you use it with PCA here, then it works but the result is converted to a Matrix

#140 would help with this, though not solve the full problem.

#139 is also related

[wildart]

Almost all fit functions accept AbstarctArray data (expept Whitening & MulticlassLDA). Problems arise from particular implementations (e.g. #140). We need to review the code to remove any type constrains, and allow to fail on missing implementations of the specific dependent functions for various array types (e.g. svd or cov)