add widget support to Jupyter notebooks

[zingale]

We should explore what capabilities widgets could offer when playing with a simulation in a Jupyter notebook.

[zingale]

idea 1: instead plotting in the notebook each step, run the calculation first, and buffer the data (at the plot intervals) and then allow the user to move through the data using an interactive slider

[zingale]

idea 2: instead of printing the whole grid of data into a notebook cell, it would be nice to be able to have a widget that shows a smal region (say 5x5 cells) and can pan through the 2-d array of data so you can explore the numerical values.

[harpolea]

idea 3: a widget for plotting the diff of two plot files. The plot itself would be interactive, allowing the user to zoom and pan, and there could be dropdowns/sliders for selecting the plotfiles and variable to compare.