Converting to @now/static-build to support now-dev for the expo app

[rlindskog]

-DON'T MERGE-

• adds a dev script to package.json with WEB_PORT=$PORT (WEB_PORT source) to forward the dev port from now dev ($PORT source)
• update now.json to use @now/static-build which looks at the dev command locally, and build when deployed.
• Properly proxy routes to the new output.
• update readme, no longer need to start expo server separately

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[alepacheco]

Thanks for the commit @rlindskog. Have you tested the changes?

[rlindskog]

Thanks for the commit @rlindskog. Have you tested the changes?

No prob! On a similar repo, let me check on this to be sure.

[rlindskog]

It looks like now-dev isn't working very well for this, might be the same problem as this issue. Might wanna hold off for a bit, not really sure what's going on but now-dev is having trouble proxying messages from /sockjs.