with-firebase-hosting improvements & fixes

[jthegedus]

Fixes #3640 (comment)

• Added _document.js & _error.js page to the pages/ to remove 404/500 errors.
• Updated deps to latest
• Consolidated all package.json files into a single root level file. This removed the need for this previous caveat:

  Any npm modules dependencies used in the Next.js app (app/ folder) must also be installed as dependencies for the Cloud Functions project (functions folder).

• Removed the need for any postinstall npm scripts
• Added babel compilation for functions/ which runs independently of the next.js babel compilation.
• use Firebase predeploy hooks to run the required npm scripts when npm run deploy runs firebase deploy.

[jthegedus]

@timneutkens Could you shed any light on why the update to Next.js v5 would force the requirement of _error.js and _document.js as per #3640 (comment) ?

Was there a change in the output dir? Or are they not built on the initial / page load anymore?

[timneutkens]

@jthegedus it's fixed in canary there was a flaw in the externals logic.

[jthegedus]

Ah okay, thanks for the confirmation 😃

When that's published we can remove those two pages from this PR and merge it 👍

[timneutkens]

@jthegedus please remove the right now, then I'll merge the example. We install next@latest always in package.json, so when it's out I can merge this example immediately 👍