Added osm_key to the result. Introduced constants.

Added osm_key to the result.
Introduced constants.
Added license header (apache 2.0) to the newly added files.

Note: I don't know, if such refactorings are welcomed.
Especially the osm_key field was important for me.

Replacing Strings with constants comes down to personal style. If such refactorings are desired, I will add them in future commits. Please provide feedback.


Thank you