replace signal handler with event handler

[mmckerns]

As stated in ticket #62, signal.signal can only be run from the main thread. Catching signals, as done in the mystic-0.1a1 release, is not suited for distributed or parallel computing... or with a GUI front-end. An event handler that understands TCPIP connections needs to replace the use of the python "signal" module.

[mmckerns]

This ticket replaces tickets #9 and #62.

Requirements (carried over from ticket #9):

• must be able to accept programmatic commands (i.e. from a script)
• must be able to use a programmatic trigger (i.e. is "CTRL-C" ok?)
• must be able to trap extension code from python (or worse, interact with a job that launched with os.system)