* Make properties optional generic
* Write tests for generic usage of gGeoJSON feature properties
* Apply layout like recommend in the tslint default rule-set.
* double quotes
* 4 spaces indent (no tabs!)
* Remove jsdoc typings and force typescript version 2.3 for sub type-definitions of geojson
* apply change of andy-ms in PR #20933
* remove empty comments and set typescript version to 2.3 to fix linting errors
* Add myself to the list of authors
* Set TypeScript version to 2.3 for packages depending on geojson