Better disclaimer for heimdall-demo

[ejaronne]

for heimdall-demo.mitre.org, please add a clear message that this is not to be used for real work and is the server version demo! I've had a sponsor incorrectly think this was a real deployment of Heimdall Lite.

Change:
"Welcome to Heimdall, a security results viewer"
To:
"DEMONSTRATION VERSON ONLY. This is a demo of Heimdall SERVER edition. DO NOT upload real data to this demo! Operators/developers can download and install their own server by visiting https://github.com/mitre/heimdall."