Add Url Helper

Add PrepareUrl helper method.
Clean UrlHelper.

- Add license.
- Fix comments.
- Rename UrlHelper method.
Updated Settings.StyleCop.

Removed `ElementDocumentationMustBeSpelledCorrectly` rule for now.
Updated XML comments.

- Added some missing comments.
- Replaced "id" with "ID".
Renamed DbContextRepository `ObjectSet` to `DbSet`.