Update Route Inspector to ignore non AspNet based routes

Initial fix for #365 Can no longer access the list of Web API descriptors after installing Glimpse in our MVC4 project.

Todo:
1) Refactor duplicated code in RouteInspector
2) Refactor the ProcessWebAPIConstraintsMessage - this was only added due to differences in the RouteDirection between MVC and WebAPI
3) Legacy projects need updating
4) Need to add unit tests