Cleanup ServiceRequestBase.buildEwsHttpWebRequest()

The old implementation seemed to be a 1:1 port of C# code, that took into
account all kinds of crap that only happens in C#'s HttpWebRequest (see [1],
which was also mentioned in the original code), like I/O delays on the creation
of OutputStreams. The new implementation could still use some work (e.g.,
signing is completely unsupported, the outputstream is cast to a
ByteArrayOutputStream (was already in the original code)), but at least this
code is readable.

To be honest, I'm wondering why anyone is even using the project. The current state
seems to be a 1:1 port of the C# library, which did not really help the maintainability
or reliability of the project.

[1]: http://www.wintellect.com/blogs/jeffreyr/httpwebrequest-its-request-stream-and-sending-data-in-chunks