Install node-pathwatcher from our branch.
fix typo in a comment
Decompose common dev_bundle build logic and variables.
Source build-dev-bundle-common.sh in generate-dev-bundle.sh.
Add script for building node separately.
Add script for building mongo separately.
Download pre-built node and mongo build artifacts from S3.
Don't remove the rimraf dependency from pathwatcher/node_modules/.

One of the actual dependencies (as opposed to devDependencies) of
pathwatcher (fs-plus) depends on rimraf, but it doesn't get installed in
pathwatcher/node_modules/fs-plus/node-modules/ because it's already
installed in pathwatcher/node_modules/, so we should avoid deleting it.
Instantiate require(console.js).Console lazily.
Implement funcUtils.coalesce(delayMs, callback).
Use pathwatcher.watch to trigger rebuilds and restart the server.

Fixes #2135.