minor refactoring, better exit handling in server
better inactivity timeout; fix #20
update server; update settings; rename emulators

changes:
* Better settings and credentials loading
* Server now handles of 'socket already in use' error
* Server no longer subprocesses emulated devices
* Previously unreachable exit code now resides in server.exit_handler,
but is still pretty unreachable.
* my.studentrnd electronic fund transfer now relies on urllib for http
GET datastring-construction.
* server now only sends letters, numbers, and simple punctuation in the
inventory response. Closes #19