Preload assemblies during Glimpse Runtime startup

To solve issue #462 we needed a way to make sure that assemblies that are dynamically loaded get pre-loaded on startup, otherwise functionality available inside them wouldn't be discovered after a recycle of the application and the way ASP.NET handles restarts.

This pull request is the implementation of [a suggested solution](https://github.com/Glimpse/Glimpse/issues/462#issuecomment-21167955)