(Feature) 721 toolbar

[Agupane]

Closes #340

Includes

• Add toolbar cofor erc721 app.
• Refactor: move erc20 & erc721 folders under /src/components.
• Refactor src/components/common/toolbar.tsx: extract common code (layout) into this component. Erc20 & erc721 apps will add their own content.
• Refactor src/components/account/wallet_connection_status.tsx: similar case as the toolbar refactor.
• Move adblock_detector to each sub-app's general layout (check the comment in index.tsx).
• Dummy search collectibles component.

It should look like this:

Does not include

• Implementation/styling of dummy search collectibles component. The styling should be implemented in the corresponding "search" issue.