[snap.auxil.ExamineSnap] several changes for clearer functionality:
[snap.auxil.ExamineSnap] several changes for clearer functionality:

- fixed method __is_identified
- new method __update_config_attr
- __update_config: only update attributes and don't overwrite them
- __read_snap_properties: code simplification by using regex pattern
- replace path placeholders like ${demPath} in auxdata properties in
method __read_snap_properties instead of __update_config
- added documentation

johntruckenbrodt/pyroSAR,johntruckenbrodt/pyroSAR