Idea for debug aid for NetworkTrigger objects

[jackjansen]

One of the problems with the NetworkTrigger and the other subclasses of NetworkIdBehaviour is that it is very difficult to make sure the NetworkId fields have all been initialised correctly and consistently.

Here is an idea to help that.

• We implement a ping or touch event that all NetworkIdBehaviour subscribe to. They set a field touched=true when touched.
• We implement a Unity editor extension command Touch All Networked Objects. This will find all NetworkIdBehaviour in the scene and have each emit a touch message.
• We use this command while running, in a multi-user session. This should touch all remote instances of every local NetworkIdBehaviour. Any one that doesn't exist remotely should give an error message there.
• Now, remotely we run Ensure All Networked Objects Touched. This enumerates over the NetworkIdBehaviour objects and ensures each one has touched==true.
• We could also run it locally (on the machine where we touched) to ensure the commands are also executed locally.

@ashutosh3308 @malte-khora (and maybe @troeggla ?): comments please...