[ux] improve account select modal: walletAddress, interactivity

[niklasp]

1. For verifying if a triggered tx is from the correct account, I was looking for a place to see the account address of the currently active account.
   a) There is some space next to the Polkadot Identicon in the accounts modal that could hold the address / trimmed version of the address on smaller screens.

b) Hovering the active account on the main view could also show a popover with the address

2. When trying to change accounts, hovering one account adds an active indicator by adding a border. Clicking the lower part of the account, that shows the free amount however does not trigger an account change.

Happy to implement the parts that find agreement.