Provide a framework for overriding default config values, persist them across application restarts

[vivekuppal]

Any config values changed in the UI will be persisted to override.yaml.
This has the following benefits

1. Persist any changes done in the UI across application restarts
2. All user changes can be isolated from application default values

Misc other changes in the PR

• Optimize the Config, Global vars singleton object constructors. Skip processing in constructor once they are initialized.
• Introduce a utilities file for common utility methods.
• Add recursive dictionary merge capability to utilities file.