Huge Jekyll Assets update. It now includes support for source maps, support for native `<img asset> tags, is faster but also no longer uses any of the previous tags. Everything is now grouped under `{% asset %}`.  Seems to work ok but requires a `npm run clean`.

1. Added .vscode exclusions to workspace settings.
2. Added sprockets and uglifier with `require: false` to provide compatibility with jekyll-assets.
3. Added `bundle install` to npm install command.
4. Updated README with issues.
5. Changed typescript output from ES6 to ES5 with ES6 libs for uglifier compatibility. https://github.com/angular/angular/issues/14595#issuecomment-330097660
6. Removed `bundle update` from CI script so that it gets gems versions from the lockfile to prevent gem update issues.