[BIG] Enforcing PEP8 on the plover/ files.

So this is kind of a large commit, but I felt it was needed to keep the code clear and readable. If it takes too long to read and merge, or conflicts, tell me. I'll rebase it myself against the master.

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"