Cleanup work

Remove User POCO and switch to using shared IdentityUser for EF
Rename claimstype options to ClaimsIdentityOptions
Cleanup overloads for IdentityBuilder
Yeah I filed a bug tracking this name issue because its a bit cludgey, IdentityClaimsOptions works, but what it really is doing, is configuring what the ClaimTypes we use when creating a ClaimsIdentity, i.e. the User Id => ClaimTypes.NameIdentifier.  User Name => ClaimTypes.Name, etc.  Its already under IdentityOptions, so none of the other child options have an Identity prefix, so we could just call it ClaimsOptions, it only is used by the ClaimsIdentityFactory below, which is why I named it as such.