Fixed Kronecker product of column vectors

Array comprehension returns a 2D array, so I added an explicit 
vectorization after the list comprehension and reordered the 
comprehension indices to get the proper result.
Multiple fixes to kron

Fixed issue 2637, and added support of Kronecker product between 
Vectors and Matrices.
Added tests for Kronecker product

Added simple tests for Kronecker product involving Matrices, 
Vectors and scalars.
Fixed bug in my implementation of Matrix/Vector Kronecker product
Simplified Vector/Vector kron and reverted Matrix/Matrix

Simplified Vector/Vector `kron` following 
@andreasnoackjensen's suggestion, and reverted the changes to 
Matrix/Matrix `kron` due efficiency of implementation, as pointed 
out by @JeffBezanson and @andreasnoackjensen.
Added support for Matrix/Vector & Vector/Matrix kron

Both falling back on the Matrix/Matrix case already implemented
Merge pull request #2646 from marcusps/kron-fix

RFC: A _working_ fix to Kronecker product