The `tracker-sandbox` tool is now a thin wrapper around the `tracker`
CLI. Effectively, this commit removes all functionality except the old
'--shell' mode. This way we avoid duplicating code paths and we make
sure that everyone is using and testing the `tracker` CLI.

The sandbox tool now captures all log output from the Tracker daemons,
instead of having them print directly to stdout. The old behaviour is
now enabled with the `--verbosity=` argument.