Revert "Minimal implementation of activity streams", we have finally to chosen to implement activity streams with rest requests to graasp

This reverts commit f83d2bde5a53a64edfcf70d47cbcb6b96e7cfe95.
Revert "Add missing import, remove broken imports", we have finally chosen to implement activity streams using rest requests to graasp

This reverts commit dd6ab87c67deb591442e101c065cf7d77a97851c.