* Make endpoint middleware explicit
This change makes the endpoint middleware explicit again, and updates
all of the templates.
The other change here is make UseEndpoints be the place where you
register endpoints. This is vital because it puts your code visually at
the point of the pipeline where it executes.
Lastly, I removed support for UseMvc with endpoint routing. This is
causing issues for some security features, and we're moving in the
direction of trying to make the middleware heavy implementation required
in 3.0. There are some issues we won't be able to fix in MVC if we can't
unambiguously know if UseMvc was used or the middleware.
John Luo
Javier Calvarro Nelson
Ryan Nowak
Chris Ross
Pranav K
Nate McMaster