refs #806

Remove useless trailing \
Remove trailing spaces
Add missing empty lines

autopep8 -ir -j2 --select=E301,E302,E502,W291,W293,W391 .

Diff quickly checked.

Change every mention of MAINTAINER to avoid future issues.

There is now a "latest" collection (or "latest_nsfw").
The feature didn't look much used, since it didn't work on many
backends.
Using collections will make it easy to support other things
like most viewed, featured, etc.
As a bonus, I added tests for every backend with the feature.

I used autopep8 on some files and did carefully check the changes.
I ignored E501,E302,E231,E225,E222,E221,E241,E203 in my search, and at
least E501 on any autopep8 run.

Other style fixes not related to PEP8:
* Only use new-style classes. I don't think the usage of old-style
  classes was voluntary. Old-style classes are removed in Python 3.
* Convert an if/else to a one-liner in mediawiki, change docstring style
  change to a comment something that wasn't really appropriate for a
  docstring.
* Unneeded first if condition in meteofrance