Fixes CTCP (reply) PING.

Replace time.ctime() with int(time.time()), and check if
 message starts with PING rather than *is* PING.
Modules now have another callback: on_numeric

Also replace the default on_command(..., mod=False, admin=False)
 with on_command(..., mod, admin), as they're always passed.
Strip leading and trailing spaces at in title.py
PEP8
Update travis environment: check with flake8 instead

We now also need to be compliant with pyflakes,
 The max line length of 119 characters remains.

tox.ini added so we no longer need --max-line-length=119