Done

XWIKI-10643: Allow the start and stop ports, and additional Java options for the standalone Jetty package to be specified using environment variables
- Using an explicit setting of default value for JETTY_STOP_PORT in BASH, since the standard short-hand way makes the Velocity parser (performed by the xwiki packager plugin) crash.

XWIKI-10650: Having a XWIKI_OPTS environment variable defined breaks the start_xwiki_debug.sh script
Fixed.

[misc] Windows scripts shouldn't be marked executable, because they can't be run on systems that respect the execute flag, and Windows doesn't care about the executable flag

Done.

XWIKI-10648: Remove the log warning about JSP support not being available when starting the standalone Jetty server
Done.

Done.

XWIKI-10646: Make the standalone debug script start in Windows even if JAVA_HOME is not defined and Java is not on the PATH
Done.

Done.

XWIKI-10644: Configure the standalone package not to send the Jetty version in the HTTP response headers
Done.

XWIKI-10643: Allow the start and stop ports, and additional Java options for the standalone Jetty package to be specified using environment variables
Done.

Done.

* Implemented using the PAUSE command which should work on all Windows versions

+ fixed all pom.xml license headers which for some reasons were not noticed with previous version of the license plugin (maybe a bug that has been fixed)

This reverts commit dd4d2ff5.

+ refactored the jetty tools under a single directory structure