Add "Please wait/loading" message when finishing wallet creation

[leafcutterant]

After verifying the mnemonic, there is a 2-3 second freeze before showing the newly created wallet (generating addresses I think). For smoother user experience, a "Loading, please wait" type of message could be displayed with some neat rotating icon. Even better would be telling the user what is going on, like "Generating addresses, please wait..." – increases user trust.