StNodeCollector: add API to choose which inspector node class to use

[StevenCostiou]

For instance, doing collectNodes or collectTempNodes always use the same kind of node, while sometimes it is necessary to use custom nodes.
For instance, I would like to do:

(StNodeCollector on: context) collectTempNodesAs: StDebuggerContextTempNode

For now I have to duplicate some code, which is wrong.