Don't merge nodes in the rendering pipeline

[tomwilkie]

Fixes #1212

This make an almost 50% reduction in the cost of the rendering pipeline, reduces memory usage by 20% and makes a big difference to garbage load.

Unfortunately is breaks everything. So we need to fix that....

[tomwilkie]

@paulbellamy I think this should all work now. PTAL

[paulbellamy]

Having read over it in more depth, and understood stuff a bit better, I think I prefer having the propagation of HostNodeID in MapContainer2Pod (the only place it's needed), with a comment saying why. Same for IsConnected in MapProcess2Container (if that's the only place it is needed?).

That way it's more explicit, and "obvious" where/why we're doing this.

[paulbellamy]

Everywhere we use ProcessRenderer we wrap it in a ColorConnected(ProcessRenderer). With this change, we might be able to move the ColorConnected into the definition of ProcessRenderer, so it is always included.

We depend on it in render/detailed/summary.go:196, to determine if a process is "linkable" so (if possible) it would be very good to have consistency there, and make sure we don't "miss" it anywhere.

[tomwilkie]

@paulbellamy PTAL?