ConnectionManager now storages Request * (not generates ids for it),
Requests have control on their RequestState, RequestIdPair is now called
Response and storages Request * with some response together.
All related classes are changed to use it in more clean and
understandable way.
Request, RequestState and Response are carefully commented/documented.
Well, it takes two API calls instead of one now, but there are no
problems with expired token because of it.
This commit changes Storage::streamFile() to pass NetworkReadStream *
through callback.
It reads the passed NetworkReadStream and prints its contents onto
console (for now). It would be writing contents into file.
To simplify work with raw NetworkReadStream there is a new CurlRequest.
It basically does nothing, but as ConnMan handles transfers only if
there is an active Request, you need some Request to get
NetworkReadStream working. Thus, there is a CurlRequest, which is active
until NetworkReadStream is completely read. CurlRequest also has useful
addHeader() and addPostField() methods in order to customize the request
easily. Use execute() method to get its NetworkReadStream.
DropboxStorage implements streamFile() and download() API methods. As
DownloadRequest is incomplete, it is not actually downloading a file,
though.
