Added Credential entity
Rewrote FindByUserNameAndPassword to use creds
Rewrote FindByUserNameOrEmailAndPassword
Added AuthenticateCredential service method
Started on ReplaceCredential
Added tests for AuthenticateCredential
Fixed up Create/Delete/PublishPackage APIs
Finished adding Api tests for new creds table
Updated GenerateApiKey action to use new table

(and to clear out old and busted API key)
Changed GenerateApiKey action to update old col
Updated Password-management service methods
Rescaffolded CredentialsTable migration
Fixed Account action to display API Key from cred
Tests are passing again
Updated ApiKeyAuthorizeAttribute tests to verify usage of cred table
Final clean-up and verification of merge
Added code to migrate SHA passwords properly
Added PopulateCredentialsTask. Also removed Identifier column for now
Merge branch 'anurse/1389-credentialstable' into dev

Conflicts:
	tests/NuGetGallery.Facts/TestUtils/MockExtensions.cs