Add ability to disable specific Pitest mutations

[martinmladenov]

It may be useful to disable certain mutations per assignment, e.g. per line number + mutation type. Pitest has support for this.
This would allow us to completely exclude equivalent mutants (rather than simply accounting for them in the grade calculation). It would also let us disable mutants causing infinite loops, which would speed up the mutation coverage calculation.

[mauricioaniche]

If not mistaken, there's already a method in the RunConfiguration to explicitly list the mutants to run.

[rstular]

The method in RunConfiguration can only disable a mutation for the entirety of an assignment, not a specific mutation occurring on a specific line number.