Revert "Changed user ID from a Guid to a "UserId" enum"

This reverts commit baaf9ab62f7f989e01d829dcc0eae17baeca34ef.
Renamed UserBase, Identity

An identity is not always a user
Added system account identity
Moved current user into identity area
Made Infrastructure an area
Removed seed data class
Moved HtmlHelpers into Infrastructure
Set IdentityDbContext's initializer to null

This avoids a database unexpectedly being blown away.
Scanning for registries instead of adding manually
Applied btn-primary class to default submit buttons