* Change languages build to use less memory
Add graceful-fs so no ned to worry about fs limits
* Specify encoding for fs.readFile
Use eachLimit since graceful-fs handles that now
* Support npm@5 and yarn
Use package.default.json
Partial #6008
- Overwrite package.json with package.default.json values
- `dependencies` field is merged with package.default.json version taking precidence
- `./nodebb upgrade` automatically does those things and runs `git pull`
- use `./nodebb upgrade --dev` to avoid the `git pull`
* added logic to preserve extraneous plugins installed in node_modules/
* Don't automatically git pull
* Simplify package-install, run it on upgrade just in case
