Load extensions in ModuleCache.create
Enable extensions for installed packages
Merge pull request #3909 from atom/ks-extension-cache-for-packages

Add extension cache for installed packages
Cache package metadata in main package.json file
Use proper relative paths in cache
Use _atomPackage key from main metadata
Only use cache for bundled packages
:lipstick:
Don't pretty print package.json

It is now ~400k pretty printed and ~300k without
Update task description
Remove inlined files from app directory
Use absolute keymap/menu paths
Remove unused properties from metadata

Saves another ~50k
Build path manually