Add a simple signup form

Add a simple form and server that logs signups
in a text file in a json format.
Fix: Make css paths relative
Use production port
Remove users route
Ignore empty entries
Stay on same page when entry is empty
Move config into separate file

Specify port number and output filename
in config.js.
Fit nicely on an iPhone screen

iPhones are 320px wide, so be less
wide than that.