[BIG] Enforcing PEP8 on the plover/ files.

A few fixes here and there:
- lines < 80char
- spaces around operators
- unused imports and variables
- `duck` replaced with repr(duck)
- comparisons with None, True, False, replaced with "is", "is not"
Merge pull request #68 from mike-perdide/pep8_fixes

[BIG] Enforcing PEP8 on the plover/ files.