feat(in place): support in-place mutation

[nicojs]

Add --inPlace flag (or equivalent in stryker.conf.json file). When inPlace is true (default is false), mutations are written "in place", overriding the user's own files. This way, Stryker can support more exotic project configurations, where even copying to a temp directory breaks the test run. For example, when a project relies on app-root-path or uses the NODE_PATH environment variable.

Support for --inPlace added in the Sandbox class. For each file that changes, it writes a backup to a ".stryker-tmp/backup123" directory. After mutation testing completes, the backup files are recovered from the backup directory.

Stryker tries its best to recover the backup files and when the process exits unexpectantly, for example, using CTRL+C or by closing the window. This behavior is a best-effort since Stryker can't do anything for you when you kill it from the task manager or with kill -9.

Fixes #2163

Todo:

• Add unit tests for unexpected-exit-handler.ts
• Update unit tests for stryker.ts
• Update unit tests for sandbox.ts
• Add integration test for moveDirectoryRecursiveSync
• Verify that all e2e tests run with inPlace mode active.
• Don't use system temp dir, instead use .stryker-tmp.
• Refactor stryker-registry to use constructor and dispose