Better model

- Updated the timeseries model workflow in several ways

    - Added computation and reporting of residual tSNR.

    - Improved the colormaps used for reporting summary statistics about the
      mode (residual variance, R squared, etc.)

    - Improved the plot showing correlations between confound and task
      variables

    - Otherwise improved the logic and testing of the model workflow.

Closes #17 
Closes #18 
Closes #24