Unify the workflow of creating a new wallet into a single multi-step dialog

[BitcoinWukong]

As mentioned in #932, the current process of creating a new wallet is very fragmented. Depending on the choices a user makes, about 8 different popups could be involved in the process.

It would be a much better user experience if the whole process is organized into a multi-step dialog, where the user can press "next" and "previous" buttons to navigate through these steps and make changes to their decisions.

Furthermore, this would pave the path for us to further unify the process of "open a wallet" and "create a new wallet" into one single dialog, so that the user could have all the choices available in a single dialog.