Debugger: Add hook for variable value writing.

WriteValueNodeJob:
- Implement async job that creates a ValueWriter to update a variable
  value on request.

UserInterfaceListener:
- Add hook for requesting that a node be updated with a new value.
  Implement in TeamDebugger by scheduling a WriteValueNodeJob.

src/apps/debugger/controllers/TeamDebugger.h

@@ -73,6 +73,9 @@ private:
 	virtual	void				ValueNodeValueRequested(CpuState* cpuState,
 									ValueNodeContainer* container,
 									ValueNode* valueNode);
+	virtual	void				ValueNodeWriteRequested(ValueNode* node,
+									CpuState* state,
+									Value* newValue);
 	virtual	void				ThreadActionRequested(thread_id threadID,
 									uint32 action, target_addr_t address);