Adapt 2d redistribution

[pat-schmitt]

Here I add some changes to the redistribution function, made by @afisc.

This includes:

• thickness threshold for filtering out spikes in the area
• rolling mean smoothing the area to avoid steps (due to the trapezoidal bed shape of the flowline)
• monthly interpolation for a higher temporal resolution

Something to discuss is if we should use the monthly interpolation as the default. Currently, there are two different time coordinates used in gridded_data (time and time_monthly) depending on if we use monthly interpolation. This maybe could be simplified if we say we always want to use monthly time steps in the redistribution.

Additionally, I added an option for an area evolution plot (show_area_plot) for finding the best smoothing parameters for your glacier. Here are some small examples:

No smoothing:

With thickness threshold of 1:

With thickness threshold of 1 and rolling mean smoothing with window size 4:

These changes should also be added to the tutorials (https://oggm.org/tutorials/master/notebooks/beginner/distribute_flowline.html).

• Tests added/passed
• Fully documented
• Entry in whats-new.rst