+ use absolute module import in stackSentinel.py and stackStripMap.py to allow for pythonic calls
- e.g. stackSentinel.main() and stackStripMap.main()
+ contrib/stack/README.md: update installation note to add $ISCE_STACK to $PYTHONPATH
+ alosStack: use $ISCE_STACK/alosStack to replace $PATH_ALOSSTACK for style consistency
Co-authored-by: Zhang Yunjun <yunjunz@users.noreply.github.com>