Refactoring controllers logic in frontend

[manuasir]

Hi splunkers, this PR refactors view controllers in frontend. The main changes are the following:

• Separate current services.js into two new modules:
  • API Service: Handles and manages all relating to interaction with Splunk backend API.
  • KVStore Servicee: Handles and manages all relating to KV Store database service.
• Implement services as abstract classes
  • Service methods shouldn't be instantiated.
  • Use static in class methods.
• Deleted unused dependencies in controllers.
• Fetch third party libraries from CDN instead locally.