Focus Order for Photons and Layer Model screens

[arouinfar]

Related to #220. Alt input is technically working on the Photons and Layer Model screens, but the focus order is currently jumbled which makes the sim difficult to use. @jbphet please let me know if you have any questions.

Photons Screen
The Photons screen should have the same focus order as the Waves screen. The only additions are the Flux Meter checkbox and slider, which should slot in like this:

• Energy Balance Checkbox
• Flux Meter Checkbox
• Flux Meter Slider
• Cloud Checkbox

Layer Model Screen

• Start Sunlight Button
• Control panels working top-down:
  • Solar Intensity Slider
  • Surface Albedo Slider
  • Absorbing Layers NumberPicker
  • Infrared Absorbance Slider
• Temperature readouts working bottom-up (matches the order the layers are added)
  • Surface temperature checkbox
  • Layer 1 temperature checkbox (first layer added, closest to ground)
  • Layer 2 temperature checkbox
  • Layer 3 temperature checkbox (last layer added, farthest from ground)
• Energy Balance checkbox
• Flux Meter checkbox
• Flux Meter slider
• Zoom out button
• Zoom in button
• Controls across the bottom of the screen working top-down, left-right:
  • Temperature Units RadioButtonGroup
  • More Photons checkbox
  • PlayPauseButton
  • StepForwardButton
  • Normal/Slow RadioButtonGroup
  • ResestAllButton

[jbphet]

This is now implemented. @arouinfar - please check it over and let me know if you see any problems.

[arouinfar]

Thanks @jbphet! Everything looks good in master, closing.