Move to PyInstaller (**breaking change**)

We use esky and cx_Freeze (or py2app on macOS) to package and update Drive releases.

But esky does not support Python 3 and is quite complexe to install, use and extend.

We could use something more reliable like PyInstaller:
1. an easy installation;
2. a uniq way to build releases on GNU/Linux, macOS and Windows;
3. a simpler setup.py, which would be quite interesting;
4. code-signing executables.

—

In addition, we need a Windows installer. We will use Inno Setup with a lot of advantages:
1. No more modifications into regedit with Python
2. Easyli expandable (customers could customize their installers)
3. Installation more than easy (click on Next, Next and OK)
4. No more admin rights required (NXDRIVE-601)
5. Installer with our logo and colors
6. Complete uninstaller (Drive files and regedit purgation, but not personnal files)
7. Good informations and logo in the panel configuration (NXDRIVE-512 and NXDRIVE-448)
8. Possibility to sign the package
11. Installation via CLI possible
12. We can build the installer via a batch script
13. Update is easy, just download the new version and click on Next, Next and OK
14. [We can remove esky and purge the monstruous setup.py]