Issue 1751 and 1741: Setting odata.metadata ContentType.Charset in OData responses

Issue 1751: OData V4 Responses MUST include the odata.metadata parameter(odata.metadata=full,
odata.metadata=minimal or odata.metadata=none) to specify the amount of metadata
included in the response in V4
https://aspnetwebstack.codeplex.com/workitem/1751

Issue 1741: Charset parameter should not show in Content-Type in response if Accept in request
don't has it

Rewrote SetDefaultContentHeaders in ODataMediaTypeFormatter to fix both issues.