refactor config.js as es6 class

[msimerson]

• refactor config.js as es6 class
  • making this a good PR to read the diff with the -w option
• bump version
• use path.resolve instead of ./dir/file (portability)
• watch: recursive=true, fixes Subdirectory config file not reloaded Haraka#2566
• permit retrieval of fully qualified path, fixes Path for tls credentials Haraka#2521

change made