Prepare master for eZ Publish 5.4.0-alpha

### Description
With these changes master (our development branch) becomes 5.4.0-alpha (our November 2014 release), and with it the minimum PHP requirement is increased to PHP 5.4.4 (the version used by Debian 7), meaning PHP 5.3 (which reached end of life from php.net some time ago) support is :recycle: as we are confident RedHat 7 will be out before November (if it does not there is also newer PHP packages via [RHSCL](https://access.redhat.com/site/documentation/en-US/Red_Hat_Software_Collections/1-Beta/html/1.1_Release_Notes/chap-RHSCL.html#sect-RHSCL-Features) available with 3 years support). In addition this PR adds support for running our tests on HHVM (:tada:) as a first step towards supporting it, and same for PHP 5.6 (:ice_cream:) 

### Todo:
- [x] Remove PHP 5.3 testing
- [x] Enable PHP 5.6 testing
- [x] Enable HHVM testing, but allow to fail as it will take some time getting it to run
 - [x] Fix segfaults found when running tests on HHVM so test suites completes, but let HHVM (Facebook) deal with segfaults and bugs caused by their implementation like [missing DOMText::getAttribute](https://travis-ci.org/ezsystems/ezpublish-kernel/jobs/25280484#L277)
 - [x] Bump Doctrine to v2.5-beta for HHVM support
 - [x] Bump StashBundle to v0.4 (supports HHVM)
- [x] bump legacy (composer and version info, done by @bdunogier in ezsystems/ezpublish-legacy#991)
- [x] Optional: Go over other dependencies and attempt to use newer versions if available.

### FAQ:
Q: What about Database versions?
Q: What about web server support?
A: Support for newer versions of MySQL, MariaDB, Apache and Nginx [added in 5.3](http://share.ez.no/blogs/core-development-team/5.3-to-come-with-broader-platform-support-and-improved-performance)

Q: Will eZ Publish 5.4 support HHVM?
A: Official HHVM support will most likely not happen in 5.4 itself, as HHVM has a long way to go to be able to run legacy code, with low test coverage, flawlessly. So this is intended for [eZ Platform](http://ez.no/About-eZ/Blog/Introducing-eZ-Platform-And-Its-New-Development-Cycle).

Q: When to expect the next increase in requirements?
A: Next expected PHP version requirement bump (to PHP 5.5 :sunrise:) is possible next year when Debian 8 [is expected](https://lists.debian.org/debian-devel-announce/2013/12/msg00008.html) to come out in stable release.

Q: Does this mean my PHP 5.3 based setup (like Redhat) is not supported?
A: No, eZ Publish Platform 5.3 that just came out fully support PHP 5.3 and Redhat 6.x, and will do so for 3 + 2 years from release day. However if you would like to use eZ Publish 5.4 coming out by end of the year or community versions after this has been merged, the recommended version will instead be PHP 5.5 which provides a speed improvement and noticeably lower memory use compared to 5.3. As for Redhat, newer versions of PHP are available via RHSCL.