Test utils should also use spreadsheet notation

[filipsch]

The tests make heavy use of utility classes such as Mutation, Deletion etc to mutate the student and solution data and then verify these variations against SCTs. If the operations are specific to a range, this range is specifed as a row and column index. However, there are utils in sheetwhat that neatly transform e.g. "A1" into (0,0).

The proposal is to have classes such as Mutation and Deletion also take in the more human-readable 'range specification', making use of the translation utility behind the scenes, so tests become easier to read and reason about.