Get rid of content.json - was cloud rclone update worker

[pisuke]

Set up an app engine to run at set intervals (1 hour?) or on file updates to generate content.json files.
Alternatively set up the player to generate the content.json files at regular intervals while not playing.

[paulharter]

• researched change callbacks for files
• created and deployed simple GEA app

[pisuke]

@paulharter @InBrewJ Better to do it with a different fix where we remove content.json tracks from GDrive and generate them with Server.py in the player container.
For filtering out content.json files, rclone offers good filtering rules.
https://rclone.org/filtering/

[paulharter]

creating content listing on the fly in the player instead

[pisuke]

@paulharter Just added a line to avoid showing up hidden files and dirs. Seems to work well!