Move packages directory out of data directory

${nuxeo.data.dir}/packages/ directory has nothing to do with the data: its coherence is linked to the server content.
In case of server upgrade (data kept) or server reset (data removed), packages directory must respectively be removed (server changed but data kept) or kept (server kept but data removed).

So move it out of data directory into the server directory.
That solves the issue with server upgrade currently requiring a reset of the packages state.

It could be nice to also include the directory used by the wizard (currently is ${nuxeo.home}/setupWizardDownloads/).

Take care to manage the upgrade (automatic removal of data/packages if exists).

Without this task :

• inconsistencies between the server and the data when upgrading, reseting data, customizing data, restoring data, ...
• issue (as explained by Sun) when customizing the data directory and needing to install DM/DAM/...
• overall work on the packaging side (Debian, zip, ...) to properly manage upgrades