Improve Styling Options / Make Application Themeable

[Moogly]

The default style for ASP .NET Core applications uses Bootstrap. It would be worth adding some new styles users can choose from. A pattern must be defined to make it possible for users to choose different styles.

[Moogly]

Found this link which may be relevant later on for this:

http://benfoster.io/blog/asp-net-core-themes-and-multi-tenancy