exercise registration, logging in/out, etc.

[thatmichaelpark]

• [x] logout logic
• [x] checkAuth to keep unauthorized peepers out
• [x] login logic
• [x] register new user
• [x] log in automatically after register
• [x] add validations
• [x] redirect from index for logged in users

[thatmichaelpark]

All done!