bayestar_sky_map.h: use COMPLEX16 instead of double complex

- For compatibility with C++
Minor fixes to executable Python script generation

- Always generate installed python_wrapper to ensure it's up to date
- Install python_wrapper in $(pkglibexecdir) instead of $(pkgdatadir)
- Use sed to filter PYTHONPATH before prepending, as per user env. scripts
- Check that input Python source file does not already have a #! line
- Remove @PYTHON...@ replacements from old LALApps Python scripts