Many rpc calls when subscribe to an event

[ferranbt]

This is issue is a follow up for the one in the old repo issue. The number of rpc calls of the polling method makes impossible to us to use api.subscribe.

[wnz99]

I think there is also an issue with the unsubscription. After some testing, it seems that api.unsubscribe(id) is not working as expected. The callback function continues to be called.