Use a good logging mechanism

I am not able to see the logs in the `.ptop.log` file.

A better way would be make a directory named `.ptop` and add separate log files under it. For the sake of preventing memory flooding, we have to have some cycling/cleaning mechanism of log files.

Need to see what are the best practices for usage of logging module.

**Observations**
- Current behavior is that only INFO level logs are made to the log file and upon termination/quitting of ptop the log file is erased.