Notifications improvements

[lukasschor]

List of non-sticky and sticky notifications: https://docs.google.com/spreadsheets/d/1McBmkEKDUIEFec0pvsz46bXpxL5j9dC74wdfLhVw_bY/edit#gid=0

Most of the notifications are already implemented but need to be checked if they behave according to the requirements in the spreadsheet.

TO-DO:
Notificacions are done, but at some point Metamask will stop reloading dApps when the network is changed in the extension. We should store the keys of the notifications related with the wallet connection and network (there is no need to store the restof them) in redux, so we can close them when some events (provider update) happen.
The basic structure is done, but not working.

[lukasschor]

@germartinez Users are confused that the "Transaction / Owner Change / ... Pending" Notifications have a green checkmark. This suggests the action is completed, but in fact, the transaction is still being processed. Could we use a loading spinner instead of the checkmark? If that's not easy to implement, we should replace the checkmark with the yellow "!" icon.

Also, I would change the wording for all policy changes (owner changes, threshold changes) no matter if 1-oo-n or m-oo-n threshold to say "Policy change pending". The reason for this is that the "More confirmations required..." part is confusing as this very confirmation is still pending and only after that, it becomes even relevant that other confirmations are needed. Also, the type of policy change is not that relevant as the user just initiated it and knows what it is about. So it's more important that the notification looks recognizable thuse the same wording across policy changes.

There are some other improvements that we could do in a future iteration of the notifications, but I think this ones are easy fixes that we should include already now.