Removing all nengo python files

Clearing them for rewrite based on code from nengo_ocl
Continuing removals: neuron/ subdir
Partial init of reference from nengo_ocl

A basic test of making an ensemble using the old_api.py works,
but probes are not implemented, so I can't even verify the output yet.
Things are at a very early stage.
More initial work on reference from nengo_ocl

- Fixed many bugs since last commit
- added decoder calculations.
- next is working on connect fn
Cleaned up base.py

* removed old nengo_theano wrapper stuff
* added docs
* added less-global random-state thing for generating weights (should del)
* added rate-mode populations
Fixes galore, test_old_api.py has working test
Adding support for multi-dimensional signals

The case study for doing this is a new CircularConvolution template and test.
Added dtype attribute to SignalView
SignalView.__getitem__ supports slice
Pretty-printing for base.Filter
Default dt=0.001 for base.Model
Suppress known NaN manipulations in step_lif
First draft of Signal indexing support
Some early steps implementing the new API
with OpenCL objects

- Also renamed James's opencl stuff
Merged James's and Trevor's work. Tests run!
Removed out-of-date comment from old_api
Cleanup test dir

Running nosetests in the project should now
* complete successfully
* pass >= three tests
* skip the rest of them.
Reorganization of nonlinear.py

Moved Sim* classes to simulator.py, but kept math in nonlinear.py
Upgrade old_api.py to use refactored sim objects

Mainly this is work in the Ensemble-creation logic.
Implement old_api make_input using Direct mode