Summary:
The prod build was failing because it couldn't find the .babelrc.
I decided to put the babelrc in the main nylas-mail repo with the
expectation that it'll need to be in the open source version too. To DRY
up this for us building, we sylink the root one to the client-app babelrc
Also since we now dereference symlinks we don't need to do the full copy
of nylas-private-resources so we don't have two error reporters floating
around
Test Plan: npm run build-client
Reviewers: juan, spang
Reviewed By: juan, spang
Differential Revision: https://phab.nylas.com/D3993
