Fix #7, direct mode functionality added

- Ensembles handle two modes: spiking (default), and direct
- Direct mode ensembles use origin, instead of ensemble_origin
- test_direct added
- basal ganglia template modified to use direct mode input / output
- network class formatting cleaned up in connect function
- TODO: add update function to origin, change input and simplenode,
  and ensemble.update to interact through this function for consistency
- TODO: add rate mode