Add watch capability

[bergerx]

It would be really helpful if we implement a watch functionality to see the updates in real-time.

But watching an object and doing queries to other resources and rendering them may cause printing inconsistent/non-correct/invalid states. Some updated on the objects are applied quite fast, it's also better not to overwhelm kubernetes apiserver.

It may be better to implement after having a shallow flag implemented in #186 and when the watch is set, the shallow mode can be implicitly enabled