Use QMAKE_TARGET_BUNDLE_PREFIX to build bundle identifier

Currently the bundle identifier is build using com.yourcompany +
QMAKE_BUNDLE. This patch adds the handling of
QMAKE_TARGET_BUNDLE_PREFIX to build the bundle prefix.

Task-number: QTBUG-19006

Change-Id: I014279da6dbef393b0df36f6d4995e40ab105316
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Liang Qi <liang.qi@digia.com>
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
network: add support for the SPDY protocol

Currently the only supported SPDY version is 3.0.

The feature needs to be enabled explicitly via
QNetworkRequest::SpdyAllowedAttribute. Whether SPDY actually was used
can be determined via QNetworkRequest::SpdyWasUsedAttribute from a
QNetworkReply once it has been started (i.e. after the encrypted()
signal has been received). Whether SPDY can be used will be
determined during the SSL handshake through the TLS NPN extension
(see separate commit).

The following things from SPDY have not been enabled currently:
* server push is not implemented, it has never been seen in the wild;
  in that case we just reject a stream pushed by the server, which is
  legit.
* settings are not persisted across SPDY sessions. In practice this
  means that the server sends a small message upon session start
  telling us e.g. the number of concurrent connections.
* SSL client certificates are not supported.

Task-number: QTBUG-18714

[ChangeLog][QtNetwork] Added support for the SPDY protocol (version
3.0).

Change-Id: I81bbe0495c24ed84e9cf8af3a9dbd63ca1e93d0d
Reviewed-by: Richard J. Moore <rich@kde.org>