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 
@dangoor It depends on where we want to put the folder. `FileUtils.getDirectoryPath(FileUtils.getNativeBracketsDirectoryPath())` returns `[install-path]/www` so your suggestion would put new folder *inside* the `/www` folder (i.e. `[install-path]/www/bundles`). But, I wanted it to be a *sibling* to `/www` (i.e. `[install-path]/bundles`).