Display of errors

[anufrievroman]

Need to implement a system to propagate errors and display to the user.
For instance, if some of the files were not loaded, there should be a message to the user or at the very least a log file.

[nfultz]

I noticed this when in the codebase yesterday playing with ICS config.

• first step is to replace print()s at

  calcure/calcure/configuration.py

  Lines 297 to 302 in fe6203a

  	except Exception:
  	ERR_FILE1 = "Looks like there is a problem in your config.ini file. Perhaps you edited it and entered a wrong line."
  	ERR_FILE2 = "Try removing your config.ini file and run the program again, it will create a fresh working config file."
  	print(ERR_FILE1)
  	print(ERR_FILE2)
  	exit()

• Also would be nice to (optionally) log exception and stack trace.

See also https://docs.python.org/3/howto/logging.html

[anufrievroman]

Implemented 020aa70 basic logging of errors and warning into log file and console.
In the future, should also display the errors in curses interface, at least after the start of the app, or maybe just a message like "Errors occurred, see info.log file".

[anufrievroman]

Commit 868c3ea adds display of error notification in curses interface.
So the issue is resolved. Maybe later the errors could be summarized more explicitly. Maybe I'll also introduce the same notification for incorrect input from the user.