Fixes FAST runtime errors

Now that enough of FAST TCP was implemented to test, I ran some
simulations, and fixed all of the errors that I was getting.  I have yet
to investigate whether or not it behaves as expected, but more complex
test cases should be coming soon.
Adds FAST support to gui, network modules

The gui.FlowDialog now takes and correctly processes TCP parameters for
flows.  Likewise, the network module now initializes Flow's properly
again.  I also updated test.ZERO to use FAST TCP, and process.Flow's
docstring.