Add loadConfigFromYaml() in TopologyBuilder

[nwangtw]

The function loadConfigFromYaml() is responsible for loading topology and component configs from a yaml file. TopologyBuilder should maintain an internal config object for topology configs. Component configs should be set to component declarers by declarer.addComponentConfig()

• The function should be called after DAG is constructed (setSpout, setBolt, etc).
• HeronSubmitter should be responsible for merging the hardcoded configurations and the loaded configurations.
• The configurations in the yaml file should overwrite the hardcoded configurations.

An example is required. Unit tests are required.