Fix for #1277 - Add Options/Startup API for WebAPI shim

Adds an options class, as well as a default options setup that will
configure the default set of formatters.

Currently most of what options needs to do is a placeholder, but it later
do things like add ApplicationModelConventions, filters, formatters, model
binders, etc. Those will be added in follow up items.
@pranavkm @yishaigalatzer is the change to `AddMvc()` for beta? I'm going to ignore this unless we're also changing MVC now.