Issue 336 2

These patches consolidate the parse of command line options to ConfigManager.
In addition, it also parses a configuration file.
> Probably It won't be needed. However, the reference manual of g_option_context_parse() explicitly describe the condition in which 'error' is set. In this situation, the above code is a conservative way, isn't it.

OK. We choose the conservative way.
If we choose the way, we should also add `NULL` check to the below `g_error_free()`.