Fix for issue #3944 : upgrade tool should support the click-through license
Fix for issue #3945 : Need to way to determine if a license had already been accepted

With this modification, the upgrade tool display the license if the
<INSTALL_DIR>/Legal/license_to_accept.txt is present into the new zip
file (issue #3944).

We also create the file <INSTANCE_DIR>/Legal/licenseAccepted when the
license has been accepted (issue #3945)
setup tools (GUI and CLI) create it after the server configuration and
before data creation (backend) upgrade tool creates it in the unzipped layout.