feat(reporter api): unify reporter api with mutation-testing-elements

[nicojs]

This change brings the Reporter API more in line with the schema of mutation-testing-elements. It also adds the metrics result to the onMutationTestReportReady for convenience.

Old	New
MutantStatus.TimedOut	MutantStatus.Timeout
mutant.coveredByTests (boolean)	mutant.coveredBy (array, an empty array means not covered)
mutant.testFilter (array)	mutant.coveredBy
mutant.testFilter (undefined)	mutant.static (true/false)
mutant.runAllTests (boolean)	mutant.static (true/false)
mutant.errorMessage, mutant.ignoreReason	mutant.statusReason
mutant.nrOfTestsRan	mutant.testsCompleted
mutant.id (number)	mutant.id (string)
MatchedMutant	MutantTestCoverage (name change)

This has also a small impact on the TestRunner API, because the Mutant is used there as well.

BREAKING CHANGE: Changes to Reporter and TestRunner plugin API of Stryker

Fixes #2766