Refactor cop attributes handling

* Pass essential attibutes to Cop.new rather than setters
* Store config in cop instances rather than classes
  so that we can remove the global state Cop.config
* Pass entire config to each cop to allow FavorModifier
  to refer to config of LineLength

TODO:
Cop#processed_source is stored as instance variable just for
processing of #inspect_file, and Commisioner needs to set
proceessed_source before processing.
This is considered bad design.