Remove trailing spaces

This pull request does nothing except remove trailing spaces.  My editor (PyCharm) is configured to strip trailing spaces and every time I do something it changes everything and it's driving me bonkers.

FYI, I did this by temporarily moving the .git directory out of the main dpark directory and then:

```bash
find dpark -type f -exec sed -i 's/ *$//' '{}' ';'
```