web/application: instantiate the repository outside of CubicWebPublisher
This improves decoupling and allows ``CubicWebPublisher`` user to choose which
argument are used during ``Repository`` instantiation. In particular is allows
caller to provide a ``TaskManager``.
The `vreg` argument of publisher is made mandatory. See CubicWebPublisher
docstring for details.
Related to #2249513
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/server/ usr/lib/PY_VERSION/site-packages/cubicweb
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/hooks/ usr/lib/PY_VERSION/site-packages/cubicweb
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/sobjects/ usr/lib/PY_VERSION/site-packages/cubicweb
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/schemas/ usr/lib/PY_VERSION/site-packages/cubicweb
debian/tmp/usr/share/cubicweb/migration/ usr/share/cubicweb/