Installation: please loading screen is not present on std Jahia bootup - no check is jahiainstallation was already done once priorly

Wehn launching the jahiaserver.bat there is no "please wait - server loading" message (same as jahiaInstallation.bat - cf scrrenthsot1).

Warning: such a boot-up screen should be configurable by sysadmin for the std Jahia bootcase. When the server crashs under load, the sysadmin should be able to switch the message and add its own customized message easily. There should be no mention of Jahia on such a page (so just a "Please wait - server is loading" only msg).

There is also no check to know if the Jahia server was already configured. So by mmistake a lot of users will immedialteyl launch the Jahiaserver.bat batch file and... nothing.... So we should add an error msg for such a use case scenario