Add "animation" for date selection

[rod-glover]

Add a control that would programmatically increment (or decrement) date (month, year) selection.

Elements: Start, stop, increment (months), speed (seconds, but see below).

This control should not go faster than data loading can accommodate. Will have to add callbacks (e.g., onDataWillLoad, onDataDidLoad) to DataViewer to accommodate this; not a complex ask.

[rod-glover]

Is this really wanted? It might well have been my own idea.