Sharing simulation bugs

[lpareja99]

• [x] Stop allowing to share a simulation to be shared with yourself
• [x] Don't allow sharing for non-owners of the simulation
• [x] Fix being able to share a simulation to a user more than 1 time. (can share an infinite amount of times to the same person)
• [x] Only allow those with permission (shared/owner) to view a specific simulation id (right now anyone can modify the URL)