client.html updates (#136 et al.)

1. Redisplay QR code for existing account if needed (master
authentication required)
2. More security enforcement
  a. First account on new steward must be master
  b. Master authentication required to create any new account
3. UI tweaks.
HTML5/D3: Activate location/distance arc labels (#163)

Active link to a map to show single or multiple locations, depending on
available data for the device.
still more "robust" authorization
client.html: allow QR code redisplay only via https: (#136)

Secure authentication on port 8888 required.