Correct the ExecShell for system-wide installs in the NSIS script
The normal portable install and the system-wide one have a slightly different hierarchy: I decided to copy the content of the Browser
directory directly in the target directory (we would have only the Start Browser
link in outside it, which I decided to not create for the system-wide install).
However, I forgot to update the NSIS script, and system-wide installs aren't actually started.