Support XML formatting

[pietersap]

With respect to my comments in issue 103

We should add support for xml formatting by doing the following:
-add the XML formatter (install the nuget package and add it in the mvc configuration)
-change ICollection to List in CarDetailsDto.cs

The result is a API that is exactly the same, except that every operation can easily return XML if the Users requests it in the Accept header. If the user does not include a Accept header, Json is still returned.

[pietersap]

Created a branch for this, we can merge it in the future if we ever want to support XML.

[MassimoC]

@pietersap before doing the Code i would like to discuss the guidelines. I cannot see your comment in the #86 Am I missing something?

[pietersap]

@MassimoC #103, edited.

Yes, this issue is open for discussion of course, I have not created a PR