Cleanup tst_Files::fileUploadDownload.

Fix expected_fail by removing wrongly used QSignalSpy.

The test failed few times already because of a timeout. The test do not
measure the backend performance, which seems to be a bit low, so we can
wait 20 sec for a thumbnail.

Fix indentation.
Shared build fix.

The EnginioBackendConnection needs to be exported for autotests.
Merge pull request #190 from bbandix/master

Re-authenticate in the EnginioBackendManager if the service url changes.
Use a const static int instead of a macro.
Move EnginioString to a separate file.
Merge pull request #191 from nierob/master

Small fixups
Fix reading the WebSocket handshake HTTP reply
in case it does not arrive at once.
Strengthen the unpredictability of the masking key

Use the whole uuid by XOR-ing each 4 byte of it together
to create the 32-bit key that is needed.
[EnginioBackendConnection] Add support for large payloads.
[EnginioBackendConnection] Handle PING and PONG messages

Additionally make it possible to send PING messages and receive
notification about PONG's from the server.
Test ping operations in notifications tests.
EnginioBackendConnection should not have its own EnginioClient

This way we can share the EnginioClient in the EnginioModel where
we will make use of notifications in the firs place.
Fix compilation on Windows.

MSVC is not handling QStringLiterals well.
Merge pull request #192 from bbandix/websocket

Websocket improvements
Merge pull request #193 from nierob/master

Partial fix compilation on Windows.
Fix the build with MSVC

MSVC does not behave nicely with multi-line QStringLiterals so
use QLatin1Strings and string builder.