Tools to maintain the Brimcap root

[philrz]

The entries in the Brimcap root are JSON files with opaque names that contain pointers to the filesystem location of loaded pcaps. I expect users may appreciate having a way to remind themselves of what's been imported, remove old/unneeded ones, and so forth, without having to create their own tooling to parse the JSON files. Following the pattern of what we've done with other CLI tooling, I could imagine this being provided by commands like brimcap ls and brimcap rm.