Design for read-only SSBC editor

Created by: eseliger

The editor page is the first tab of 3 in the execution of a batch change.

• When you are executing and coming back to this tab, it should be read-only - and buttons and such should be gone
• There needs to be an indicator that it is read-only
• We want to make sure the user knows that something is already executing (just the tab non-disabled doesn't do it for me)
• we want a button to allow "Cancel current execution and start editing again"

This ticket also involves the design for the "replace spec" modal that opens when you select an item from the library pane.

• The modal when you click an item from the library pane now shows the contents of the spec that the user would be replacing theirs with, giving them the chance to copy from it if they want
• When the editor is in read-only mode, the "replace" button in the modal is disabled with a tooltip