Do something about the unwieldy ExperimentInstance constructor.

[haacked]

The constructor for ExperimentInstance has a lot of parameters. Because we want this to effectively be an read only instance, we need to supply all the parameters via the constructor.

Our options are:

1. Create a new ExperimentSettings class that has settable properties. Add a constructor overload to ExperimentInstance that takes a settings instance and sets all the properties accordingly.
2. Create a new ExperimentBuilder class that lets you set properties and returns a new instance of ExperimentInstance with those properties set via some Create method.
3. Add multiple ctor overloads to ExperimentInstance
4. Something I hadn't considered...

/cc @davezych who noted this problem

[joncloud]

I created a quick implementation of 1. I figured i'd keep it simple, but we can definitely cook up another implementation if it seems more suitable.