Add SSH tunneling and explicit launcher declarations in ~/.Pickett.json

This is the "big leap" that is the smallest possible incremental step towards remote launchers.

With this change, all communication to launchers is done through SSH tunneling, the parameters of which are stored in ~/.Pickett.json (or the file specified by --localConfigFile).

An explanation and example is added to the README.
My only comment here is that  "local configuration" is a very confusing term for per-user configuration.

I would think that local == per project, global == all projects. So actually $h/.pickett.json is a GLOBAL configuration file.

My suggestion: one is a config file (the one in your home directory), the other is a project file (a la "Makefile").