for every plot type years should be optional

[rabutler-usbr]

years should always be optional

• [ ] if they aren't specified at the global level, then guess current year through 2060 and post message.
• if they aren't specified for the ind. plots, then use global years.
  • [x] standard plots
  • [ ] heat
  • [x] cloud
  • [ ] 5 year simple
  • [ ] individual plots