Omega/state time level change

[sbrus89]

This PR changes the time level interface in the State class to be consistent with what has been implemented in Tracers.
The new functions getLayerThickness and getNormalVelocity retrieve the device array corresponding to a given TimeLevel. getLayerThicknessH and getNormalVelocityH provide the same functionality for the host arrays. All time index calculations for a given TimeLevel are done in the function getTimeIndex. A getTimeIndex function has been added to the Tracers class as well.

Checklist

• Documentation:
  • Design document has been generated and added to the docs
  • User's Guide has been updated
  • Developer's Guide has been updated
  • Documentation has been built locally and changes look as expected
• Testing
  • A comment in the PR documents testing used to verify the changes including any tests that are added/modified/impacted.
  • Unit tests have passed. Please provide a relevant CDash build entry for verification.