Feature: Preview line editing

[desplesda]

The preview interface lets you play a Yarn project from within the editor. However, when you make a change to the source code of any of the Yarn files, the project must recompile, and because the compiled byte code has changed, the preview must reset.

One of the most common reasons for using the preview feature is to try out the dialogue and see what works, narratively speaking. It's quite often the case that a writer will spot a change in a line's phrasing, and will want to make the change in-place.

The editor should allow the following flow:

• Lines and options in the preview view should be able to enter an 'editing' state.
• In this editing state, the text of the line is editable.
• When the user commits the change, the Yarn file that that line or option came from is modified to incorporate the change, and the preview view updates to show the modified text.

In addition to making textual changes, this flow could also be used to add 'to-do' markers and other metadata, inserting #todo hashtags or similar on a line while doing a proofreading pass.