Enable FxCop code anayzers under project properties, and add an editor.config

[SimonGeering]

Is your feature request related to a problem? Please describe.
Ensure that all contributors to the codebase adopt a common coding style so it is easy to pick up any code in the app and work with it if someone is familiar with the codebase.

Describe the solution you'd like

• Enable the built-in Microsoft Rosalyn Code Analyzers for FxCop under project properties dialog.
• Add or generate an editor.config for the solution.

Describe alternatives you've considered
Don't have an alternative, it would have to be a lot of effort in PR reviews!

Additional context
None.

[benrick]

Yep, we definitely want an editor config to make it easier for people to keep consistent code.