First draft of context system and object syntax
Fixed the two examples
Changed context stack behaviour

Now any time a model is created it clears the context stack
and becomes the new default.
Quick fix to get spike probes working
All connections now stored in model

- Rather than on pre/post
- Removed all connections_in/connections_out code.
- Also fixed some unit tests that were failing.
Using ContextStack data structure

- ContextStack is a collections.deque subclass
Cleanup and PEP8 fixes

- Everything now follows PEP8
- Moved ContextStack to __init__ and removed context.py
- Moved Network class to objects.py to make importing cleaner
- Made some relative imports absolute imports,
  will try to always do this in the future