Bump master (development) eZ Publish version to 5.4

Master is now 5.4.0-alpha, and the following commits will remove and add support
for the platforms we aim for for 5.4 release.
[HHVM] Enable hhvm testing in .travis.yml

But specify that it is allowed to fail, as further fixes are
needed in both ezpublish-kernel as well as hhvm before it will
pass.
[HHVM] Change boostrap.php to not have to copy config.php

Will allow our tests to run on HHVM's framwork tests, as it does
not allow any initial steps to be perfromed other then composer
installs and running phpunit.
[HHVM] Bump Doctrine-DBAL to 2.5beta & -Bundle to 1.3beta

This is the version of Doctrine which is adjusted for HHVM and where
they aim to offically support HHVM. Unsure when it will reach stable.
[HHVM] Change CoreBundle KernelTest to not mock Stash DriverInterface

As interface declares __construct which does not work with phpunit mocking and HHVM.
Might be fixed in phpunit 4.x, but phpunit upgrade will need lots of other fixes.
Removed PHP 5.3 support

PHP 5.3 is no longer supported by PHP.net, and we expect new version
of Redhat to arrive before we release eZ Publish 5.4 in the fall which
this change wil be part of.

In the meantime we would like to start to take advantage of PHP 5.4 featurs
for eZ Publish 5.4.

We will move further to PHP 5.5 when Debian comes out with new release in 2015.
Add PHP 5.6 support
[Temp] Also test on hhvm-nightly
Bump package versions to 5.4
Bump StashBundle to v0.4
Merge pull request #862 from ezsystems/bump_to_54

Prepare master for eZ Publish 5.4.0-alpha