EZP-23067: As a community user, I want to have access to the PlatformUIBundle

JIRA: https://jira.ez.no/browse/EZP-23067

# Description

The goal of this patch is to prepare the PlatformUIBundle to be public.

# Tasks

* [x] Remove the wrong and useless version number in the YUI test modules
* [x] Update the README
  * [x] Clearly separate the requirements for running it from requirements for developing it
  * [x] Install with composer
* [x] Add a license header in source code
* [x] Configure Travis (need to be tested, can not be done until the repo is public)
* [ ] ~~Generate the API doc and put it online~~ (will be done in a separate PR if time)