Aquilon-related schema should be released with the broker

[jouvin]

As mentioned by @jrha several times, in particular in quattor/release#326 (comment), it is painful to have the Aquilon-related schema distributed by the template library as it means it is unsynchronized with the broker version and may make the life of sites still running older broker difficult (because the new schema may not be enforced in the plenary templates generated by the old broker).

As the Aquilon-related part of the schema has been factored out in separate templates in quattor/template-library-core#177, it would be easy for the template library to release an empty version of this schema files and have the broker responsible for adding the appropriate location in the pan include path, before thethe plenary templates area. One way of achieving this would be:

• to provide these schema files as part of the Aquilon sources (instead of the plenary template area)
• to have the broker adding the path where these schema files are located in the Pan include paths, before the plenary templates.