Touch parent folder on file modification

[elyahw]

This solves #2382

[harshad1]

I still oppose including this in mainline markor (we will have to check the effect on every sync solution etc as this is nonstandard behavior for a file manager)

That said, if the author would like to merge this into their personal branch, I would make the following changes:

1. Touch the parent folder in the Document class
2. Don't use currentTimeMillis(), instead copy the stamp from the just written file

[gsantner]

I can also suggest to guard it with try catch.

This change is at pretty much the most dangerous point of the project. You don't want to lose any file contents, just because your filesystem throws some error by touching.