Added Chocolatey packaging utilities

Everything needed to update the Chocolatey package.
(More information : https://github.com/chocolatey/chocolatey/wiki/CreatePackagesQuickStart)

Currently the package is unlisted because it's awaiting moderation, but it's avaible here : https://chocolatey.org/packages/syncthing-gtk

Since I am currently the only maintainer of the package on the website, just create an account on Chocolatey and add it to the list of `owners` in the `.nuspec`file. I'll push it as soon as I can, so you will have an access too.
Python 3 is installed by default on most Linux distributions. Also I'm studying it, never actually used it in a "real" program.

Well, I applied the diff and everything worked in the first time. Since `from __future__ import unicode_literals` didn't work alone, I was trying to use `ìmport codecs` which was messing with a lot of things... Thanks!