Use SQLite as database + stores abstraction

[nilskj]

• Swap Postgres for SQLite in database-layer
• Remove S3 asset file storage dependency and store images in SQLite db.
• Introduce isEditing and currentUser, svelte stores with abstractions to simplify prop drilling for client side state.
• Change all pages to use abstraction components, such as WebsiteHeader

Still to be done

• Revise docs in README.md