Switching over to IEnumerable

Making the switch for all returned objects from IList to IEnumerable.
Converted to be IEnumerable based.

Converted the ApiWrapper class to return IEnumerable instead of IList to
simplify as there was nothing useful about the List.

Also, moved most properties like People, Projects, etc to be "Get"
functions... GetPeople(), GetProjects(), etc. Something felt weird about
them being properties.
Fixed NUnit reference.

Changed the Test project's NUnit reference to be the nuget NUnit
package.