[Misc] Add missing license header + reorganize a bit the content to align between commons, rendering and platform + add new ignore for XVNC (found thanks to Gradle Enterprise) + removed unused weblate section

* Collect custom user data
* Secure publishing
* Add new GE ignore

* provide a Debian package to register the events core in a standalone Solr instance

* Remove old experimentation since we're starting with a new design (see http://design.xwiki.org/xwiki/bin/view/Proposal/MailModule)

Skeleton

* Add gitignore