Decouple from Laravel

According to [#194](https://github.com/Intervention/image/issues/194) I added a new manager which is used by StaticManager now. BC is not broken for now, BUT: If you are considering a new minor/major release a bit of restructure would be good. There are some code duplication now which could be simply optimized by making the 'Basic' manager the default one and using that with the laravel manager.