ERC20 and ERC721 routes split

[unjapones]

Blocked by #327: we should resolve themes things first (at least, the basics). Connects #311.

Description

To test this, you can either go to http://{host:port}/erc20 and http://{host:port}/erc721`. Accessinghttp://{host:port}` should redirect you to the erc20 app by default.

Includes

• Add directories /src/erc20 and /erc721 with sub-directories pages and components.
• Update the routing logic to suppor both sub-apps.
• Add constants to set default sub-app .
• Adapt GeneralLayout to accept custom a toolbar as a propr: erc20_app and erc721_app will have to provide their corresponding toolbar component (which is different in both apps).
• Add modal to connect metamask in erc721 sub-app (we can disable this if it is annoying while developing).

Does not include/TODO:

• Have to think about the scenarios & logic to config the routes:
  • what happens if we only need the er20 app? i.e. we don't want to access it using /erc20/bla
  • what happens with the build?
  • etc.
• The erc721 toolbar implementation is not there yet. The layout it is using the same that the erc20_app uses. The general layout should be in place though.

[fvictorio]

• Adapt GeneralLayout to accept custom renderToolbar: erc20_app and erc721_app will have to provide their corresponding toolbar (which is different in both apps).

Very minor, but maybe it would be a little better to just pass a component instead of a function, unless that function may receive some arguments from the component that uses it. What do you think?

[unjapones]

Removing the blocked-by label: rebased using development to get the Dark Theme.

[fvictorio]

@unjapones changed the base branch of the PR to erc721.