Summary:
This PR introduces the possibility to group plugins in categories.
The category can be determined by setting the `category` field in `package.json`.
Categories are sorted alphabetically.
Categories are shown below all uncategorized items.
Within categories, items are sorted as before: by last recently usage.
Design wise, the category name might now look more prominent than the app name, this is to be addressed in a follow up PR.
Reviewed By: jknoxville
Differential Revision: D18169459
fbshipit-source-id: 77deb0f27a0462a0d449944ddc262396160687a2
494ffd26b3