Split package actions from frontend components and add signals

[RRosio]

This PR

• moves package action functionality from components into a separate packageActions.ts file
• adds signals for package actions
• registers the jupyterlab commands for package modifications with backend/persistent actions
  • updateAllPackages
  • applyPackageChanges
  • refreshAvailablePackages
• removes notifications for loading packages as there is a spinner indicating the status of loading

[github-actions]

👈 Launch a binder notebook on the branch RRosio/gator/pkg_actions

[RRosio]

CI failures are unrelated and being investigated in #318