[Delivers #47641051 #47641173 #43555125]Add/Update Account Metadata functionality.Update Account Headers functionality.Get Account Metadata functionality.

**Stories:**
https://www.pivotaltracker.com/story/show/47641051
https://www.pivotaltracker.com/story/show/47641173
https://www.pivotaltracker.com/story/show/43555125

Get/Add/Update ***MetaData*** and ***Headers*** for Account.

**Integration tests** 

```C#
Should_Get_Headers_For_Account()
Should_Get_MetaData_For_Account()
Should_Add_MetaData_For_Account()
Should_Update_Headers_For_Account()
```