Allow non-admin users to add and edit their buildings

[spaceraccoon]

Resolves #314 and #311

• Removes userId attribute for user model
• Authentication now adds userId attribute to session
• Building component uses creator getter and setter to check if user is creator of building
• New /api/creator route to check on server side
• Conditional rendering of edit button now based on creator or admin status
• Server side validation of building edits now based on authenticated, admin and creator status
• Server side validation of building creation now based on authenticated (not admin) status

In sum, this creates three tiers of users:

• Non-admin: Able to add and edit ONLY their buildings
• Admin: Able to add and edit all buildings
• Superadmin: All of the above and user privilege powers