Navbar should dynamically display buttons based on current context

[kappanjoe]

• Log In should only be visible when not logged in
• Log Out should only be visible when logged in
• See My Memories should not be visible on the (my) Memories page
• See My Memories should only be visible when logged in
• Home should not be visible on the Home page
• Home should be visible on the Log In page
• Add a New Memory (not prefecture-specific) should be visible in the Navbar when logged in

CSS styling for Navbar (#26) should be resolved first.

Edit: added another task