H1 Pkg and ingredients changes

[fonsp]

I will make some separate PRs to keep things organised, this one is just technical pluto things:

• I copied the EBM code directly into H1. ingredients("1_energy_balance_model.jl") only works if the student clones the entire git repository, but until now we always had them open the homework via URL. We could do ingredients(download("https://raw.githubusercontent.com/hdrake/simplEarth/master/1_energy_balance_model.jl")) but then we face the next problem: both notebooks perform Pkg operations, and I am not sure how stable that is. I'd like to experiment with all of this another time, but right now it is a bit too risky!
• Fused Pkg.add commands into one to make it faster

[hdrake]

Thanks. I agree that for the time being we're best just manually copying the relevant code across notebooks. It would be nice to have this as a stable feature in the future, though (even if behind the scenes Pluto somehow merges all of the Pkg commands in the ingredients with those in the main notebook, or something like that).