Tweak Optimizer interfaces for consistency

[schlessera]

While writing the documentation, I'm noticing some minor consistency issues that should be straightened out at the earliest possible convenience.

I'm collecting these here to make a grouped PR for this as a dependency for the docs PR.

• The TransformationEngine's first argument Configuration $configuration should be made optional via a poka-yoke, just as the second argument is. This would then fall back to the default out-of-the-box configuration.

• The required order of the arguments when a transformer implements both Configurable and MakesRemoteRequests should be swapped, so that it matches the order of the Configuration and RemoteGetRequest arguments in the TransformationEngine's constructor.

• Docblocks in FilesystemRemoteGetRequest are copypasta from StubbedRemoteGetRequest and need to be adapted.