Add util for reading efit gfile

[f0uriest]

This PR creates a DESC input file from an EFIT geqdsk equilibrium file.

To dos

• [x] needs tests
• [x] check units and factors of 2pi
• [x] Make sure that for a non-separatrix boundary the pressure and iota profiles are truncated
• [x] Reorganize the code to make it more dev-friendly

Resolves #728