More activities events

Fix #1670 
Fix owncloud/core#7950
Fix owncloud/core#6437
Fix owncloud/core#5876

- [x] Fix file links when sharing non-root folders
- [x] Someone changes a shared file
- [x] Someone adds a new file into a shared folder
- [x] Someone deletes a file in a shared folder
- [x] Depends on https://github.com/owncloud/core/pull/8009
- [x] Depends on https://github.com/owncloud/core/pull/8132
- [x] Remove `Shared/` folder