JobComposer: Feature Upgrade: Convert script <pre> into editable pane.

[brianmcmichael]

Right now we show a preview of the script content for the selected submission script.

This would be more useful if it were an editable panel incorporating the Ace editor.

This feature currently GET's file content via the cloudcmd API. It could be saved by adding a button that PUT's edited content back to the API.

┆Issue is synchronized with this Asana task by Unito

[johrstrom]

Even though this is an old ticket applying to the current job composer, I'm going to repurpose it for the new job composer. It's that good of an idea, that users should be able to make quick edits (with no syntax highlighting) on a file in the same window that they're submitting the job from.