Fixes and additions to profile.jsonld

[pierrocknroll]

Hello,

I am developing a tool using the profile.jsonld file, and I noticed some errors or omissions that I took the liberty to correct:

• Added missing profiles (downloaded-audio, uploaded-audio, etc.)
• Added missing concepts
• Added missing rules for the downloaded-file and (un)registered-course profiles
• Removed hard-coded values in $.context.contextActivities.category.id
• Made some corrections in the statement markdown files where the JSON examples were invalid or there were typos

Since I am not the original author of this file, there might be mistakes :)

Thank you for reviewing !