Bring drafts and related actions to redux

Summary: This differential creates a place for drafts in redux, and makes actions to handle them visible for reducers.

Test Plan: Make sure eslint and flow do not point errors.

Reviewers: tomek, atul, ashoat

Reviewed By: tomek, atul

Subscribers: ashoat, abosh

Differential Revision: https://phab.comm.dev/D5644