Feature/user install

Created by: starox

Hello,

I tried to make paperwork user installable and made a working branch against stable version, fixing issue #340 (closed) The drawback is that all data files is in the egg produced by setuptools. Thus, icon and desktop file is not installed in the correct place. Note that this is the way setuptools works. It is not intended to put files outside of it eggs. I let the icon and desktop file installation aside, because I think it must be discussed.