Tajik translation updated
Update FSF address

The FSF changed its address quite some time ago. Modify the license
headers to contain the new one. Also update the central COPYING
text to the current text from the FSF homepage, which purges some
stray form feed chars in the process.

https://bugzilla.gnome.org/show_bug.cgi?id=721488
Use Python 3.x for Python plugins