Updated MacroEngineFactory to use PluginTypeResolver and made it thread safe. Have also
updated it to only create one instance of each IMacroEngine per application which should
increase performance a teeny bit, plus that's how it should be.
unit test helper classes. Changed calls from old TypeFinder to new TypeFinder2. Created benchmark unit
tests to test speed differences between them.
Fixes: 30946 - IOHelper with HttpContext issue
Fixes: 30945 - AppCodeFileExtensions issue with UmbracoSettings