Implement test command run tox
Implement test command run tox

* Customize internal test command to run tox and bypass all arguments
  of `-a` into tox itself
* Declare traditional tests_require dependencies
* Add test to extras_require
  (e.i. making possible to run `pip install cherrypy[test]`)
* Fix #1457

cherrypy/cherrypy,cherrypy/cheroot,Safihre/cherrypy,cherrypy/cherrypy,Safihre/cherrypy