Remove thirdparty/unittest2 from webkitpy and require python2.7.

This is probably already true in the code base (we mostly require 2.7
for everything except for some things in ChromiumOS), so this is just
cleanup.

I also fixed a few other nits while touching everything (sorting imports,
fixing shebangs and file permissions).

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/478553002

git-svn-id: svn://svn.chromium.org/blink/trunk@180338 bbb929c8-8fbe-4397-9dbb-9b2b20218538