forjj secrets should load or refer to a file

[clarsonneur]

If an external tool has generated a secret/configuration file somewhere in my system, I do not necessarily want to make a copy of this data to forjj, but just refer to the file, which has normally proper right for such file.

So, forjj secrets should support saying that a secret is stored in a file (reference) or copied from a file (copy), or as current, edited via an editor like vi, or last, set