GeoRSS sensor (#9331)

* new geo rss events sensor

* SCAN_INTERVAL instead of DEFAULT_SCAN_INTERVAL

* removed redefinition CONF_SCAN_INTERVAL

* definition of self._name not required

* removed unnecessary check and unnecessary parameter

* changed log levels

* fixed default name not used

* streamlined sensor name and entity id generation, removed unnecessary parameter

* fixed issue for entries without geometry data

* fixed tests after code changes

* simplified code

* simplified code; removed unnecessary imports

* fixed invalid variable name

* shorter sensor name and in turn entity id

* increasing test coverage for previously untested code

* fixed indentation and variable usage

* simplified test code

* merged two similar tests

* fixed an issue if no data could be fetched from external service; added test case for this case