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

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

danieljprice / phantom