Implementation of Rxjs

1. Simple polling
2. Combining polling with refresh button
3. Polling and reset
4. Polling when data is resolved

Operators used:concatMap, map, merge, delay, tap, skip,concat, catchError, retry

This example developed by Smitha Kommareddi based on https://blog.strongbrew.io/rxjs-polling/

rxjs 6.3.3, Angular 7.0.0