Generate CSV files for diagnostics [DRAFT]

This pull request adds:

1. `CSV` app that writes `link.csv` and `app.csv` containing time-series information about the app network. (This data is used to feed the dashboard to see what's going on.)
2. `designs/csv/csv` script to create an app network that includes CSV output.
3. Sample `app.csv` and `link.csv` files in `designs/csv/`.

This draft implementation writes a CSV record every 100ms and writes timestamps as floating-point Unix time.

The `app.lua` is currently lacking dynamic information like CPU utilization: the meat is in `link.csv`.