FS: Create a new step (rte for new email)

[skassam21]

• 

• Creating a dialog where a user can create a new step:

  • a type: "New thread", "Follow up with previous thread"
  • Subject
  • a rich text editor for the body - material-ui React editors (https://github.com/niuware/mui-rte) vs more customization with draftjs + https://material-ui.com/components/toggle-button/

• Make the API call to create the step