Upgrades

[Lewiscowles1986]

Hi,

I've used your repo to get started with LibreOffice in docker

I've the following modifications, I'd be happy to PR

* Updated LibreOffice to 5.4
* Handled GTK & GTK3 Bindings in Xenial
* Bumped from Trusty to Xenial
* Bumped to OpenJDK8
* Trimmed Image to 1.3GB (From 1.54GB)

Let me know if you're interested, if not in all, then what you'd be interested in (I mostly wanted to check the new Ribbon UI, and experiment with desktop apps in docker).

I've got it public in a Gist https://gist.github.com/Lewiscowles1986/790deceea8e08949313cb7379de9e17a