Create animations for freeze-up/break-up seasons

[tom-andersson]

Be good to have some highly visual animations of short-to-medium-term forecasts initialised in the freeze-up/break-up seasons when SIC is changing more rapidly.

Example starting point to play around with:

• Init 1st August, forecasting 2 months ahead
• Init 1st Nov, forecasting 2 months ahead

Let's also work out the optimal frame rate for demo purposes! Not too slow that people don't spot it moving, not too fast that no one can follow any details.