Option `STOPPORT`: New default `0`

[ChristianGruen]

With version 13, the new default value for the STOPPORT option will be 0, such that the Jetty server cannot be stopped with a single HTTP request anymore (unless requested).

[ChristianGruen]

Discarded (basexhttpstop and Windows’ »HTTP Stop Server« start menu item would become dysfunctional by default).