Merge pull request #196 from nierob/master

Small improvements
Add simple keep-alive timer to EnginioBackendConnection

In case of inactivity ping the server every second minute.
Creating a watchdog for reconnection in case of a timeout should
be the users resposibility.
Do not leak EnginioReply in case of error.
Set the parent of QNetworkReply in registerReply
instead of doing it all over the place.
This also fixes a memory leak since the QNetworkReply was
not parented with one of the EnginioReply constructors.
De-obfuscate the implementation of remove

It ended up being error-prone because of the ifdef.
Generate a X-Request-Id header for each request
This is needed to track the REST API requests end-to-end
and match notifications to API requests.
Make the request id header accessible on EnginioReply
to be able to use it in EnginioModel.
Do not expose the key generation function on EnginioBackendConnection
since it is not useful anywhere else but the WebSocket handshake.
Merge pull request #197 from bbandix/requestid

X-Request-Id
Change AttachedDataContainer implementation to something slighter smarter

The implementation is still bad, but it had to be cleanup a bit for
notifications support.
not working fixups
store attached data for all items
Use notifications in EnginioModel
Ignore own requests in notfications

Oh my, it works!