Detect file changed by other program

**Is your feature request related to a problem? Please describe.**
Sometimes you edit the same file in both the Frank!Flow and VSCode or another editor. VSCode will detect changes saved in the Frank!Flow and it will load the changes automatically. The other way around is not the case. This gives the risk of losing changes when you made changes in VSCode, go back to the Frank!Flow and edit the old version and save it.

**Describe the solution you'd like**
Make the Frank!Flow detect changes made by other programs an load these changes

**Describe alternatives you've considered**
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**Additional context**
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Start by tracing how Frank!Flow loads and saves files, then examine how the editor represents unsaved changes and reacts to updates from other programs. Done means external file changes are detected and loaded without silently overwriting edits made in Frank!Flow.

Written by the indexing model from the issue text.