Issue #171

server limit the number of webUI clients that can attach.

This will probably always be "0" or "unlimited", but allows ops to set a max limit for WebUI clients. (realistically, probably 3 is more than enough)

@crankycoder r?
Well, the box can only handle so many connections. so "unlimited" is never going to apply. Various platforms have various limits on the max number of sockets they can handle. Unless someone is being malicious, I don't expect them to open more than 2 or 3 at a time (thus "system limited"). If someone decides to be malicious, ops can set this flag to something like 3 and limit the number of WebUI connections to 3 per device.