Add a setting to disable the recovery/cache of files

A few hours ago I deleted a couple of files of my private folder. That was not an accident, I wanted to delete the files. I used my system `rm` command against the mounted FUSE directory.

Then I saw that keybase has a `fs recover` command. I ran the command against the same folder with `--reltime 1440m` and keybase started to recover the files.

I would like an option to disable the recovery of files and also the deletion of any cached blocks when I use a plain `rm`. I have local backups of the files and I can't use disk space for unneeded files.

No files or tests are named. Start by tracing the `fs recover` command, the mounted FUSE directory, and handling of plain `rm`; done means a setting prevents recovery and avoids retaining or deleting cached blocks as requested.

Written by the indexing model from the issue text.