Python 3 support

This would especially be great because we don't have to care about python vs python2 anymore. On distributions where python = Python 3 we would use that and on other systems we just use Python 2.


First problem encountered:
```
This Disc ID is ambiguous:
Traceback (most recent call last):
  File "./isrcsubmit.py", line 805, in <module>
    release_id = disc.release["id"]         # implicitly fetches release
  File "./isrcsubmit.py", line 433, in release
    self._release = self.getRelease(self._verified)
  File "./isrcsubmit.py", line 459, in getRelease
    release["title"]))
  File "./isrcsubmit.py", line 304, in print_encoded
    if isinstance(arg, unicode):
NameError: global name 'unicode' is not defined
```