Replaces IDirectWebRequestHandler with HttpClient in DNOA.Core.

Build breaks are everywhere outside of just this one project as a result.
Fixes build breaks in DNOA.OpenId.
DNOA.OpenId.RP now builds.
Adds HttpResponseMessage.AsActionResult extension method.
Fixes default ctor argument of identifier discovery services.
OpenID RP login actually works now.
Web Forms based OpenID RPs work now.
Fixes KeyNotFoundException in logging.
Adds another catch block to the logger initializer.
OpenID.RP.UI now builds, and ASP.NET control login works.
OpenId.Provider now builds.
Made another method async for consistency.
DNOA.OAuth project now builds.
OAuth.SP now builds.
OAuth2.Client builds.
OAuth2.Client.UI now builds.
OAuth2.ResourceServer now builds.
OAuth2.AuthorizationServer now builds.
OpenId.Provider.UI builds now.
All product projects now build.