run experiments from single command line script

note: UNTESTED, please review

the goal with this is to run experiments from a single command:

    >> pyoperantrun.py TwoAltChoiceExp --panel='Panel3' --subject='B999'

this opens up a few immediate benefits:
- we no longer need to define `if __name__ == "__main__"` for every behavior protocol 
- we no longer have to set executable permissions on each behavior protocol file.
- we no longer have to register each behavior protocol with v/zstart 
- we can now have multiple behavior protocols defined in a single file 

this approach also has potential future benefits:
- we can start isolating experiments to threads, which will facilitate closing out hardware appropriately
- by separating the behavior protocol (say, TwoAltChoiceExp) from the process that runs it (pyoperantrun.py) we are a step closer to running multiple behavior protocols from a single process and being able to stop using our old PERL scripts

rather than registering each script with our `start` PERL script, this will load any behavior scripts that exist in `pyoperant.behavior` OR it will search the packages listed in `BEHAVIORS` in `pyoperant.local`