1.0.2

Adds FixedLayout, refactors useAuth, PageLayout, Avatar

1. Moved placeholder Toolbar from app/layouts/PageLayout.js to app/core/Header.js
2. Removed Header ref from app/layouts/PageLayout.js and app/core/Header.js
3. Added sx to Link in app/core/Avatar.js
4. Using auth.isLoggedIn in PostPrompt.js & PostCard.js & Profile.js
5. Created & connected mui-demo repository
6. New auth in Header.js
7. Changed height & width in Avatar in Header.js
8. Created FixedLayout, Logo, AccountOrLoginButton. Got rid of Header