Adjust temperature plots

[sean-rohan-NOAA]

Proposed solutions to issues #7 and #8

• figtab.Rmd: Combine EBS shelf and full EBS raster layers into one rasterBrick layer for plotting.

• functions.R: Create blank data frame to plot "No Survey" on 2020 facet and drop NAs from raster brick prior to plotting (necessary after combining EBS shelf and full EBS raster layers.

  I was able to generate a 20-panel figure that looked correct, although I can't tell if this will break NBS plotting, etc. because I generated the figure using functions in the repo but not using the full workflow. Screenshot:

  

Realized that bottom temps are extremely difficult to see with the small panels and full temperature scale.

[EmilyMarkowitz-NOAA]

I added the changes suggested by this pull request remotely while on a flight, so I won't be able to properly accept the pull request. I am declining the request but know that everything you wrote here was ultimately included! Thanks for your contribution!