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 
@peterflynn I started with "bundles" just to get the code going, but I agree that it's not quite right. To me, the "bundle" is the "installer plus the extensions" (not just the extensions). Unless I hear any better suggestions, I'll change it to "auto-install-extensions" and put it in a constant.