Be able to edit the source file in the main interface

[fab918]

Please describe your proposal in a ONE sentence

One sentence describing your idea

In order to work more smoothly, it would be good to be able to edit the source file directly. An editor is already present (when loading a file), but it is not available to edit the sources.

Underlying problem

For each change in the source file, this requires opening an external editor, edit the file and save, then reloading the script and the reselecting the proof (which will create a duplicate in the proof section.)