Update MatrixTable.show

[Will-Tyler]

Description

In this pull request, I change the implementation of the MatrixTable.show method. Previously, show would create a table and then show the table by reusing the table implementation of show.

The problem with the existing implementation is that it creates row fields in the table for all of the entries in the matrix table.

This new implementation directly shows the matrix table by creating a table and displaying the information in the table.

I make some refactoring changes in this pull request as well that helped me understand the code and will hopefully help others as well.

Testing

I add some unit tests.