[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
../../doc/book usr/share/doc/cubicweb-documentation
../../doc/html usr/share/doc/cubicweb-documentation
../../debian/cubicweb-doc usr/share/doc-base/cubicweb-doc