Refactor TimelinePromptEditor and PromptInput components in frontend #60
Description
There is a bunch of duplication across these two components right now because they both contain rendering logic for the Prompts box - the former is used when editing timeline blocks eg "Edit mode" and the latter is used when appending live timeline blocks eg "Append mode". Every time we make a change to the Prompts box we need to make the same change in both components. See #58 for an example of where we had to do this and how it is easy to accidentally forget to make the change in one of the components.