Exit gracefully when pcigale.ini is not found
When launching pcigale from a directory missing the pcigale.ini file, rather than a clear indication of the issue, cigale gives a cryptic backtrace:
Traceback (most recent call last):
File "/home/mederic/.local/bin/pcigale", line 9, in <module>
load_entry_point('pcigale', 'console_scripts', 'pcigale')()
File "/home/mederic/pcigale/pcigale/__init__.py", line 104, in main
run(config)
File "/home/mederic/pcigale/pcigale/__init__.py", line 49, in run
configuration = config.configuration
File "/home/mederic/pcigale/pcigale/session/configuration.py", line 223, in configuration
self.complete_redshifts()
File "/home/mederic/pcigale/pcigale/session/configuration.py", line 286, in complete_redshifts
z_mod = self.config['sed_modules_params']['redshifting']['redshift']
File "/usr/lib/python3.5/site-packages/configobj.py", line 554, in __getitem__
val = dict.__getitem__(self, key)
KeyError: 'sed_modules_params'
It would be better to indicate what is the issue.