Add indicator showing that the Wallet data is being updated

[marcinbodnar]

We are getting closer to a moment where we will be persisting all wallet data from the previous session - the result will be that the user will see data from the previous session while entering Wallet or switching accounts.

With that, we would need some kind of indicator that will show the user that the data is being updated.

For example:
The user has two accounts in Wallet. Sends Near from the active one to the second one. Switching to the second account. The user sees the old Near amount, and after the update, he sees the new amount.

If the network is fast, the update will be very fast, but with a slow network, it might take a few seconds or longer. In this case, we would need to show the user that the data is being updated.

It applies to all data in the wallet.