exchange: dispatch all code in 'serveronly' to the appropriate submodule
All code related to exchange is now in either 'evolve.obsexchange' or
'evolve.obsdiscovery', and the 'serveronly' extension is using their 'exthelper'
to set itself up. As a side effect, the 'serveronly' extensions now enable
better exchange when pushing from that server too.
syntax: re
/figures/[^/]+\.png$
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
\.err$
^tests/easy_run.sh$
^build/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$
tests/\.testtimes