nodogsplash: Backport v3.2.1 to OpenWrt 18.06

nodogsplash: Backport v3.2.1 to OpenWrt 18.06

This release provides bugfixes and some minor enhancements:

  * reset upload/download counter when a client has been authenticated a second time [mwarning]
  * print sesssion duration as 0 in "ndsctl json" and "ndsctl clients" output when a session has not been started [mwarning]
  * rework html templater to speed up splash page generation [mwarning]
  * FAS documentation updates [bluewavenet]
  * Add CSS file and update splash and status html [bluewavenet]

Signed-off-by: Rob White <rob@blue-wave.net>