Started implementing networks

- Basically our way of doing simple templates
Added Integrator template

- A very basic template, but shows that the Network base works
- Also unit test and example for Integrator template
Initial implementation of PassthroughNode
Integrator working with PassthroughNode
Added basal ganglia network
Allow string probes to handle networks

The string syntax 'A.B' could mean to probe signal B on object
A, or to do a default probe on the object 'A.B'.  The fix here
is to check if 'A.B' exists, and if it doesn't, then try looking
for 'A' and probing it for 'B'.
Made PassthroughNodes probeable
Changed BG "Input" to "input" and "Output" to "output"
Added BG test
Initial circular convolution implementation

- Direct and neurons case working
- It can now be created independently of the model.
Converted circularconvolution to network

- Unit test exists, but no example yet
Removed templates/circularconv.py
Merge branches 'network' and 'master'