To support UNICODE xblock.location

When people use unicode course org name(e.g Chinese) ,urllib.quote cannot format unicode char like:

```shell
>>> import urllib
>>> loc = 'i4x://创联/7302478/chapter/4ab413b41ad9447db41668bed03f149f'
>>> urllib.quote(loc)
'i4x%3A//%E5%88%9B%E8%81%94/7302478/chapter/4ab413b41ad9447db41668bed03f149f'
>>> urllib.quote(unicode(loc))
Traceback (most recent call last):
  File "<console>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe5 in position 6: ordinal not in range(128)
>>> 
```
so I open this pull