Summary:
Install plugins to pending directory first to enable installing new versions of existing plugins. On startup Flipper moves all the plugins from pending directory into installed plugins directory.
Auto-update, after downloading a plugin package, will also extract it to "pending", so after restart update will automatically be applied.
Reviewed By: mweststrate
Differential Revision: D21929713
fbshipit-source-id: 141b106415e941156ae598cf810ab3bed8c76ced
eeded4e32f
