Remove ScopedAs as it's no longer relevant (the feature was cut from C# 6)
and get ExceptionContext to compile again.

More C# 6 features to abuse when I get a chance...
Add StringInterpolation file to project (should have been included before.)
(And add the file itself... doh.)
First part of "Going down the rabbit hole" code (investigating how to display
a Hebrew date/time).