python crash sometime

Hi @jwagner : using the previous version of playitslowly, I had one crash when starting playitslowly from the CLI on an udpated Debian Jessie, I had:

```
~$ playitslowly
Traceback (most recent call last):
File "/usr/lib/python2.7/runpy.py", line 162, in _run_module_as_main
"__main__", fname, loader, pkg_name)
File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
exec code in run_globals
File "/usr/lib/python2.7/dist-packages/playitslowly/app.py", line 44, in
from playitslowly import mygtk
File "/usr/lib/python2.7/dist-packages/playitslowly/mygtk.py", line 37
SyntaxError: Non-ASCII character '\xc3' in file /usr/lib/python2.7/dist-packages/playitslowly/mygtk.py on line 37, but no encoding declared; see http://python.org/dev/peps/pep-0263/ for details"
```

I then followed the recommendation here : https://www.python.org/dev/peps/pep-0263/ .
I then added: `# coding: utf-8` to the 2 files: https://github.com/jwagner/playitslowly/blob/master/playitslowly/myGtk.py and https://github.com/jwagner/playitslowly/blob/master/playitslowly/app.py and it worked again.
Since I just followed what's written on the pep-0263 but I'm not knowledgeable about python, I choose not to submit a pull request but to report the issue + possible solution here.
Hope that helps