Update classlist.json

Added an article and a demo.
Update vibration.json

Added an article and a demo
Update web-speech.json

Added a demo
Update notifications.json

Added an article and a demo
Update pagevisibility.json

Added an article and a demo
Update vibration.json

Removed trailing comma
Merge pull request #535 from AurelioDeRosa/patch-1

Update classlist.json
Merge pull request #536 from AurelioDeRosa/patch-2

Update vibration.json
Merge pull request #537 from AurelioDeRosa/patch-3

Update web-speech.json
Merge pull request #538 from AurelioDeRosa/patch-4

Update notifications.json
Merge pull request #539 from AurelioDeRosa/patch-5

Update pagevisibility.json