Hovering for node values should respond to 3D top surfaces of neurons

[StephenJRead]

This isn't really an issue, but I did notice that the active area for hovering over a node to get values is the outline on the 2 D layer surface and not the bar that graphically shows the value. This makes sense and I don't see what would make more sense, but this does have the effect that when the network is tilted, as is the default, this can make it difficult to get values for back rows when there are large values (bars) on the nodes in front. I don't think it effects the readout, but it does make it hard to see where one has to click to get a value. I also think that the naive thing for a user to do is to think that clicking on the column will always work, when it's the node outline at the base of any column that is actually active.

[rohrlich]

I see that Stephen already filed this. I changed the title as I don't agree that it is minor. It will mean calculating a second set of locations but I think it is important. Unless you are paying close attention to the unit numbers (e.g. [1,3]) and you actually count the boxes you don't know if you are on the one intended and as Stephen pointed out the hove appears broken if you mouse over the topmost row of neurons.