Update logger.php

changed Logger.php in the following ways

1. we now log the file name, function name and line number of the log message.

2. the time stamp is in its own field

3. added 4 verbosity levels: Critical, Error, Info, Debug
    
I added the verbosity level so that we can control what log messages actually get inserted into the table without having to remove or comment the callers.

This will probably prove useful when we move to prod an are not concerned with debug information. 
      
todo:

1. logger should be moved out of the database directory and into its own

2. the table name should change from paypal_log to just log

3. the already existing log callers need to be changed to use the appropriate verbosity levels.

4. Test the logger from WP pages.