Lack of support to sequenced RPC requests

[alexruzenhack]

@andreabadesso has found that the success feedback after RPC request approval doesn't allow the handling of two RPC requests in sequence, once the dismiss of the feedback sends the user back to dashboard and dismiss the possibility of other request.

[alexruzenhack]

It is not a lack of support, actually the success feedback modal can remains active if user doesn't act on it, meanwhile a new nano contract request can happen, the screen will load the information for this new request in the background and the success feedback modal will keep active.

A quick solution was to create a screen for the success feedback, see the PR: #554. But we should refactor the handling of new nano contract transaction request to create a queue and let the user manage it.