Remove Xml dependencies from ProtoCore

##### Background
This pull request is meant to address the following task:

[MAGN-2463 Remove Xml dependency from ProtoCore.Core APIs](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-2463)

The serialized trace data in a ```DYN``` file now looks like this:

```xml
  <SessionTraceData>
    <NodeTraceData NodeId="b662124a-62ca-4503-b37a-29f0ee7fe5cf">
      <CallsiteTraceData>Dummy callsite data</CallsiteTraceData>
    </NodeTraceData>
  </SessionTraceData>
```

##### Pending items for this to be fully functional
- Implement ```SingleRunTraceData(string serializedTraceData)``` constructor
- Implement ```internal string GetTraceDataToSave``` method on ```SingleRunTraceData```
- Implement ```public string GetTraceDataToSave``` method on ```CallSite```
- Implement ```public CallSite``` constructor