Add UTF-8 coding lines to all Python files

While not strictly necessary for files containing only ASCII
characters, adding a line with "coding: utf-8" can guard against
future SyntaxError's in case someone inserts a Unicode literal.

This commit adds such lines to all .py files. The syntax used by this
commit works with Python (of course). It also works with Emacs, which
will recognize the special "-*-" marker and use the "coding" variable
to correctly decode the file, even in an environment where UTF-8 is
not the default file encoding.

Existing coding lines were normalized to match the new lines added.

Partial-bug: #1325193
Change-Id: I58bf93fea711fd25890356a397e594bd820c99e3
Merge "Add UTF-8 coding lines to all Python files"