topics: add a config to reject draft changeset without topic on a server
This patch adds a new config option experimental.topic-mode.server which if
sets to True, the server won't accept any draft changeset without topic on it.
In case both `experimental.topic-mode.server` and
`experimental.topic.publish-bare-branch` are set to True, the enforce-topic one
is respected.
Tests are added for it. The CHANGELOG file is also updated mentioning about the
config option.
syntax: re
/figures/[^/]+\.png$
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
^tests/.*\.err$
^tests/easy_run.sh$
^build/
^dist/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$
tests/\.testtimes