convert dws_session to dws_session_server
ignore autogenerated dev*_vars.config files
make reltool.config.script to work even for clean

If the `rebar clean` was run, the reltool.config.script
has failed because there was no .app file.
So we started to use .app.src to avoid this issue.
When the clean is run, we don't care about version
numbers or release at all...
mnesia clustering; node discovery on foreign nodes