Implementation: spatial / temporal filter for along-track SLA data

[kdrushka]

• Implement with multiple satellites (done, via pangeo)
• Adjustable filter type (Done)
  • Gaussian
  • Sharp
  • Box
  • Adjustable but fixed filter resolution (Done)
  • Input kilometers
  • Input degrees
• Adjustable and geographically variable filter resolution (Outstanding)
  • Consider possible methods to do this