Fix format string for logging authorization code

In case the code cannot be retrieved, an error is logged that clearly
intended to log the code variable (on successful authentication is is
actually logged as well). This fixes the missing parameter placeholder
in the format string.
added allowed post_logout_redirect_uri to client reg
Merge pull request #430 from paumayr/dev

Fix format string for logging authorization code
Added kid to JWT header for asymmetric signing keys
use PathBase for cookie paths
added DisableSignOutPrompt setting added to AuthenticationOptions
return null when no signin cookie
always pass some error message to error view
Add call to exception logger
display strings from resx files
Update README.md
Initialize claims collection in InMemoryUser
removed pairwise subject type from disco doc
add flags for filtering per-client login page options
initial signin message rewrok
forgot to pass signin message ID (fixes tests)
add client name and return URL to logout pages
provide LogoutResult; clear signout messages upon logout
Start of end session validation work
Merge branch 'dev' of https://github.com/thinktecture/Thinktecture.IdentityServer.v3 into dev