Design mutation levels

[dvcopae]

[H] Xavier must support specifying a mutation configuration file, which restricts the number of mutation
operators executed in a testing run.
[H] Each mutation operator must be individually specifiable in the configuration file.
[H] Xavier must implement the mutation level specification as an extension of the existing configuration
file.
[M] If no mutation level is provided for Xavier, StrykerJS should execute a mutation run with all the
mutator operators.
[H] The preset mutation levels defined in Xavier should provide an attractive range of coverage-performance
trade-offs.

Design two/three mutation levels from Jan's paper and put them in json objects. Make sure that all the supported mutators in StrykerJS are included.