Fixes/features for new land cover legend editing functionalities

[azvoleff]

• [x] dynamically create land cover map styles from the legend saved in job json
• [x] ensure correct nesting legend is passed through to job file (right now it is doing ESA to custom legend without including the custom legend to IPCC - need both)
• [x] ensure SOC uses the correct nesting information to calculate SOC transitions
• [x] use the custom legend for land cover imports (dropping auto-reading of classes as was done before), and add functionality to land cover import screen to allow users to access/edit the custom legend from there if needed (and flagging to the user if the file they are trying to import contains class codes that are not defined in the custom LC legend)