Auto install bundle

Automatically install extensions "bundled" with installer on startup.

**Issues**:
* Should appReady in ExtensionManger be used instead?
* Terminology: folder name and location

cc @dangoor @peterflynn 

This is for #9233 
Yeah... it looks like Package easily _could_ wait until Node is ready, but it doesn't.  All the calls are wrapped through `Package._extensionManagerCall()`, but it just rejects with an error if Node isn't ready yet, instead of waiting.  Weird.  I guess Extension Manager itself relies on the fact that it's impossible for users to click fast enough to get into this code before Node has finished booting up.