Node mapping between callsite and graph UI node

Add a test case LiveRunner.MicroFeatureTests.TestNodeMapping() for demonstrating the mapping between callsite and graph UI node. 

Some key properties/methods:
* Core.CallSiteToNodeMap: from callsite's guid to graph UI node's guid
* Core.ASTToCallSiteMap: from AST's ID to call site
* LiveRunner.GetSSANodes(): get AST nodes in ssa form for a graph UI node.