Printing matrix without toString()

[ReneEnjilian]

This patch enables the DML to print matrices and other datatypes (frame, list) without using the toString() method.
Previously, printing a matrix A required: print(toString(A)).
Now, printing can be done via: print(A).
The same applies to frames and lists. However, there are some remaining issues when datastructures are used with indexing. For example, while A[1,] is also a matrix (first row of A), print(A[1,]) will not print the correct output (first row) but rather only the first element of the first row. Internally, the compiler misinterprets the matrix as a scalar and does not propagate the correct size information. The propagated size information on the rewrite-level are (-1 x -1), meaning unknown. A work-around would be either to still use the toString method or, as shown in the test cases, to materialize the slicing before printing: B=A[1,] , print(B).
Similar problems exist with lists and frames but can be addressed by materializing the slicing/indexing outside the print as shown in the previous example. A future task should address this issue.
I promoted the rewrite from RewriteAlgebraicSimplificationStatic to having a separate class in the rewrite directory as discussed. Testing has been added.

[ReneEnjilian]

All checks fail. The error message for all of the 44 failing checks is something like:
Error: fatal: unable to access 'https://github.com/apache/systemds/': The requested URL returned error: 502
Can I assume that this issue is unrelated to my pushed code ?

[mboehm7]

Yes, that seems to be an external issue, but the missing license header (failed license check) is real, and once you made this change we get another run of the tests.

[mboehm7]

LGTM - Thanks for the patch @ReneEnjilian. During the merge, I moved the rewrite to static rewrites (in program rewriter), fixed the failing test, and removed commented code.