Tweak interface for integration into atmos

[nefrathenrici]

This PR removes the sbatch scripts and replaces them with a julia interface for running calibration in src/slurm_interface.jl.

This has been replaced by a julia interface which schedules and handles sbatch jobs, located in src/backends.jl.
We now have two calibrate methods that dispatch on differing AbstractBackends, which specify the "backend" to use for a calibration run. There are two backends: Julia and CaltechHPC.

Additional Content

• Use experiment directories instead of experiment ID for ExperimentConfig constructor. This allows for calibrations to run from an arbitrary location instead of assuming the experiment folders are in the working directory
• Remove sphere HS example
• Move postprocessing/plotting funcs
• Update docs
• Add pipeline to test slurm calibration
• Update SF calibration experiment to work with new interface
• Update pipeline.jl
• Add hooks for obtaining ENV variables. This can be useful for passing information to individual processes running forward models.