Logging all information of a session in a log file for easy understanding by developers in case of a issue

We can create additional handler for file.
Our logger object will be set at debug by default and will send all logs to both handlers(stdout and file).
file handler will be set to debug and would log everything in a `cwltool.log` file.
For each session this log file will be cleared and rewritten.
we will put this file's name in `.gitignore`. So whoever files a issue can be requested to upload log file for better understanding.
stdout handler will be set to info or warning level which can be changed as per user specified debug flag.