Add a copy constructor for the Matrix class.
Once we have created the SubmatrixQueries DS, we just provide access to the already created DS for fast queries on rows and columns.
Introduce test functions.
Bugfix: the max column IS the max position.
Add some test routines.
Bugfix: I forgot a case when writing the submatrix query. We can be in the case where the query's row range does not contain any interval in a node envelope.
Add basic benchmarking tools to the test class.