Created ipython.py and matplotlib.py

- These contain functions specific to the packages
  they're named after
- Right now, ipython contains a helper to hide input cells
  - This is used in nef_summary to hide plots
- matplotlib.py contains a rasterplot function
  - This is also used in nef_summary

This also renames `simulator.copied` to `simulator.get`,
which acts more like `model.get`, to avoid having to do
sim.model.get often.
Updated neuron examples to use new rasterplot