[server/test] stop using email cube - make unittest_migractions use a separate datadir, and add a fake email cube there (we use it to test {add,drop}_cube, so need something that looks like a cube) - for the other test modules, just copy what we need from cubicweb-email's schema to our test schema

Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming

Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html