(set_star) MAJOR cleanup of setup_star into neat subroutines with high level functions

[danieljprice]

Type of PR:
cleanup of setup_star routine

Description:
Shifted most of the functionality done in setup_star.f90 into a new helper module called set_star.f90 which also replaced and incorporates set_stellar_core.f90. The aim is twofold:

• Outputs from the relax-o-matic procedure are now useable as starting files, even if stopped half-way through the relaxation. For this we needed to put the setting of the thermal energy of the particles into a new set_star_thermalenergy routine. I kept going from there to clean up the entire routine.

• in principle it should now be possible to more easily set up stars from other code modules (e.g. moddump or setup_tde.f90) with the full functionality of setup_star: namely being able to map and relax tabulated MESA stars

• with a few tweaks one could now in principle setup and relax several stars in sequence before placing them in orbits

• setup_star.f90 is now easier to read and maintain, basically just a shell handling the options read/write from the .setup file

Bug fixes / other changes:

• fixed bug reading example MESA files from the repo (phantomsetup: bug with reading the example MESA file #291)
• halved the number of snapshots written by relax-o-matic to avoid filling disk space unnecessarily

Testing:

• checked relaxation of a polytrope
• checked read-and-relax of star from Kepler
• checked read-and-relax of Passy (2012) star from MESA table (P12_Phantom_Profile.data)
• checked and debugged replace-core-with-sink procedure using an example file supplied by @themikelau

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