Establish new root and refactor communities

[elliotBraem]

Pull request regarding #294

Unblocks:
#253 - new community addon framework
#175 - telegram plugin
#268 - blog plugin
#267 - wiki plugin
#265 - github plugin
#266 - kanban plugin

Sets the stage for:
#303 - New DevHub homepage
#295 - Updates to layout and header

See a preview here and navigate to and around the Communities. (A full migration for Feed has not yet been complete, will wait for approval first)

How does it work?

It starts with a new namespace (DevHub) and a new root (DevHub.App)

Within this new root, we simulate a sort-of React Router (for BOS) that checks for a "page" prop and determines the page from this:

function Page() {
  const routes = page.split(".");
  switch (routes[0]) {
    // ?page=home
    case "home": {
      return <Homepage />;
    }
    case "communities": {
      // ?page=communities
      return (<Communities />
      );
    }
    case "community": {
      switch (routes[1]) {
          case "configuration":{
              // ?page=community.configuration
              return <CommunityConfiguration />
          }
          default: {
              return <Community />
          }
      }
  }
}

And we define our Theme and Layout:

  <Theme>
    <AppLayout
      page={page}
    >
      <Page />
    </AppLayout>
  </Theme>

---

Rather than merge this to mainnet, I'd like if #305 could be approved and this could be merged to testnet first.
Merging 305 will also unblock #301 so there can be more clean code in this refactor.