+ dem.py: replace filename in xml file with abspath after geoid to ellipsoid correction
+ update README.md files in contrib/stack/*Stack, as fixImageXml.py is not needed anymore
+ fixImageXml: use native argparse mutually exclusive group for --full/--base options to replace checking with own code
ISCE_HOME was only used to get the location of the default logging config.
Lots of scripts were using boilerplate to set up this config, so I added
an `isce.logging` helper module which is the same as builtin python logging
but already has the configuration defaults set up for isce.
ISCE_HOME setup is retained in the toplevel `__init__.py`
but can now be removed without affecting functionality.
Zhang Yunjun
vbrancat
Ryan Burns
Heresh Fattahi
Microwave Remote Sensing Laboratory
Zhang Yunjun
Eric Gurrola