Update input streams of already running / existing stream

[branimirangelov]

Use case: Hatchery

In relation with #23, the user can update the stream description on re-launch. We have to decide on behavior.

[branimirangelov]

Consider as part of #47

[bojidar-bg]

As of current master, it is possible to edit the Stream/Call's Execution's parameters manually (i.e. directly through Ignite), however there is no code handling such changes to parameters and the new values won't be used until the agent container is restarted.

As Hatchery seems to be working alright at the moment without this feature and #47 was implemented, is it still needed?

One way something like this could be implemented without additional Perper functionality is by creating a blank stream of e.g. stream arrays in the caller and subscribing to all the streams from the last item in the receiver; likewise for other types of parameters.

Removing milestone as this is not blocking for release.