Use python3 loader for media-player
Convert indentation of Python code to only use tabs.

Common Python style guides (PEP 8) strongly recommend choosing either
tabs or spaces for indentation, don't mix them.  This file mixed the
two styles, which seemed to cause strange bugs when trying to run it
with Python 3, and it also issued a warning.

Style guides seem to prefer only-spaces to only-tab.  I used only-tabs
here since that seemed to be the common style in Liferea C code, but
I'll change it to spaces (four for each level) if that's prefered.
Change print statement to Python 3 print function.

Also include "from __future__" statement so that the code will
easily backport to Python 2.6/2.7.
Use "python3" loader for gnome-keyring.  Change indentation to tabs.