I2mc

- `endT` and `dur` fields of fixation output are now consistent
- plot submodule no longer needs to be imported separately
- some enhancements to plot function:
- can now set a different unit for the axis label
- doesn't assume time starts at 0
- can now set x and y signals min and max instead of only max

two_cluster_weighting: placement of switch weights was inconsistent with locations where downsampled data were taken from, which causes a slight misalignment for some downsample levels, and also a crash due to wrong indexing for some valid input parameters (e.g. downsample 5 for 60 Hz data and a .2 s window)