Added more support new nengo api.
- Modified old api to accept IndicatorPDF's as arguments for max_rate, intercept parameters
- Added connect function to nengo.model
- Updated Uniform to subclass of IndicatorPDF
- Updated matplotlib references to plotlib
- Added ylim, xlim, yticks, xticks, grid, vlines function to plotlib module. They currently don't do anything because the Nengo plotter don't support these functions.