Revert "Merge pull request #494 from homakov/patch-2"

This reverts commit 9b76e4fb58b5870ff48ba9704432787bc2e76cfb, reversing
changes made to bf32f4bbfc5401dde48341cd5e664e2f7837d151.
Reimplement auth scheme fix

 * Add Rack::Auth.add_scheme to enable folks to fix anything that breaks
 * Add common auth schemes, MS ones, AWS ones, etc are missing, as unlikely
 * Checked Rails - they don't use our authorization code
 * Checked Warden - uses rails
 * Checked Omniauth - uses rails
 * Checked doorkeeper - users rails
 * Checked rack-authentication - does it's own thing
 * Checked warden-oauth - doesn't do headers
 * Checked devise - uses rails
 * Checked oauth2-rack - header creation only
 * Checked rack-oauth2-server - does it's own thing
 * Probably missed a bunch, but that'll have to do