Adding dynamic redirects. Fix for #793

Fix for #793 

*Do not merge this yet!!!!*

This change removes all static binding redirects in app.config, and introduces dynamic redirects in core. The way this is done is by listening to the AssemblyResolve event on the AppDomain, and loading / returning the assembly to redirect to. It turns out using this technique you can swap on the fly and give a different assembly than what was requested.

At startup, it builds a map in map in memory based on the assemblies that scriptcs ships with ensuring that any requests for the same names will be redirected to it's version. It also ensures that any packages in the scriptcs packages folder take precedence over what the script pack / packages assemblies were actually compiled against.

Assembly black magic at its finest....

It appears to work so far :-)

This does not fix the Service Stack script pack issue, as there appears to be no magical fix for that other than updating the script pack. However, I was able to get the old Web Api script pack to work with the latest Web Api (see comments)


This seems to be the wrong check. It's checking the field is null, which it always will be, and not using the parameter at all.

I think a nice pattern here for all the optional parameters would be:

```C#
_foo = foo ?? new Foo(...
```

If editing this piece of code, I would also add null guards for the other params since we are going to be de-referencing them later.