* Created `Injector` class, a readonly class that can instantiate `Injectable`s
* Updated the `PluginLoader`, so it can load plugins with the new way of working as well as provide a Bridge plugin for all "old fashion" plugin
* Started implenenting the `BroadcastReporter` and other Reporters in the new way.

Couldn't help to make some quality of life improvements:

* `StrykerOptions` now have the expected required/not required properties.
* Created "test-helpers" package so we can share test helpers between packages.

The TestInjector is a new way of creating your System Under Test (sut) objects.
You can configure what to inject and then call `TestInjector.inject(SutClass)`

Also added some unit tests for the Injector class.

* Made the context of the Injector generic.
* Made injector readonly and type safe
* Moved all injector related stuff to its own package: 'typed-inject'
* Updated TestInjector class to now use the new typed-inject
* Updated Stryker to now use the new typed-inject
* Updated Stryker-api to now use types from typed-inject

…d move implementation of functions to stryker-util

…t it in its own PR

…method.

…r plugin

Move all stryker plugin stuff back to the api. Talked about it with Simon. We'll allow small pieces of implentation code in the api, as long as it doesn't have any side effects

…plugins

…onfig-editors

…creators

…onfig-editors

…onfig-editors

… factories