Debian package fixes

1. Use --with python2
2. Add build dependency on Python.
3. wrap-and-sort control, copyright and install files.
4. Fix installation location for goopg-chrome.install
About debian/copyright,

can you please also add information about the "doc/icon.svg" file? (see AUTHORS for more info)

I forgot it... 

Otherwise, don't worry, I will do it by myself...