Move AllowAnonymous to Microsoft.AspNet.Authorization

[Eilon]

It's a bit odd that [Authorize] is in Microsoft.AspNet.Authorization yet its companion attribute [AllowAnonymous] is in Microsoft.AspNet.Mvc. They should both sit together in the same place.

@Tratcher @HaoK @blowdart @rynowak FYI.

[NeelBhatt]

Exactly my thought!!

[ajaybhargavb]

aspnet/Security@0f78135 and 6bd97c7