add --json flag to apm ls
grab package metadata from package.json as well
Use better syntax for checking callback existence
:lipstick:
Always pull bundled package metadata from _atomPackages

This fixes a regression when the package metadata cache
was originally introduced and the versions no longer were printed
for bundled packages in apm ls.
Keep options sorted
Nest listing of installed packages
Merge pull request #216 from atom/dh-ls-json

WIP: add --json flag to apm ls