FGData Merge Request #216: Change various effect paths to load textures for the SpaceShuttle AI scenario (merged)

This patch fixes various path in the xml files of the SpaceShuttle AI landing scenario preventing the loading of various textures and ac files. Tested on 2020.3.5.

It also removes some executable bits on various xml files within the AI/Aircraft/SpaceShuttle/ directory (+ truman_demo.xml) which should not be there (probably set by accident on a windows system?). See commit logs.