Added new overload for Call method on DeskApi. Allows caller to create their own RestRequest and have it executed.

Refactored some methods in CompanyMapper to use the new Call method.
Added a couple of tests for CompanyMapper.

Refactored CompanyMapper to get rid of private methods that returned IRestResponse.
Removed code that was commented out.
Removed constructor from Company class because it was not being used.
Modified .gitignore to ignore packages folder.

Enabled NuGet restore on solution.