AthleteDirectory - Folder Structure Part 2 of 2 + Always create .JSON

... create folder structure for existing and new athletes
... upgrade existing athlete to new structure when opening / incl.
logging and error handling
... convert any "Downloaded" file to .JSON directly - store source file
in /downloads
... convert any "Imported" file to .JSON directly - store source file in
/imports
Merge pull request #1111 from Joern-R/files1

AthleteDirectory - Folder Structure Part 2 of 2 + Always create .JSON