disable/enable of year slider section

- on load it is disabled
- if the data only has one year (or has no year column) then it will
  remain disabled.  (Note that there is no separate visual indication
  for this case)
- once data with multiple years is loaded, you can enable/disable using
  the switch.

Still need to

- reload all data on disable via switch.
- enable/disable year dropdowns on switch
finish disable/enable year range functionality

when the year slider is enabled, disable the year range form element,
and put some text to make it clear that is disabled.

Also as soon as the switch is changed, change the data displayed from
data for all years, to data for just one year.

And vice versa for both.