Create a cross platform standalone install package

We need to drastically simplify the first installation of XWiki.

1/ The standalone install package should use jetty and hsqldb
2/ It should work on Linux or Windows or anything else.
3/ The only dependence should be on Java (1.4 or 1.5).
4/ It should include a default database in an export package.

It should be installable by Java Web Start or from the command line.