(setup_star): unclutter warnings; warn if relaxation not converged

[danieljprice]

Type of PR:
Bug fix / cleanup

Description:
This is a cleanup of the setup_star procedure, containing the following changes:

major:

• moved read_mesa and read_kepler_profile into separate modules containing
  functionality for read/write of mesa and Kepler files

minor:

• uncluttered warnings, in particular added line spaces before and after ALL warnings in phantom
• added warning if the relaxation procedure in setup_star did not converge
• setup_star now dies if it fails to read the MESA EOS tables, instead of seg faulting
• fix build failure in phantomsetup due to set_hierarchical (if make setup typed before make)
• make all warnings in checksetup emit "ERROR: " or "WARNING: " to make them more obvious
• only print the centre of mass from checksetup if there are no warnings or errors, to avoid clutter around important warnings
• a few other minor cleanups (use id==master for MPI; remove commented code and unnecessary printouts)
• simplified Makefile for phantomsetup

Testing:
Tested on .setup file setting up a MESA AGB star, supplied by Chunliang Mu

Did you run the bots? no

Did you update relevant documentation in the docs directory? no