ac64cec gui: create wallet: add advanced section (Sjors Provoost)
c99d6f6 gui: create wallet: name placeholder (Sjors Provoost)
5bff825 [gui] create wallet: smarter checkbox toggling (Sjors Provoost)

Pull request description:

  Previously only users who needed a second wallet had to use to the create wallet dialog. With the merge of bitcoin#15454 now all new users have to. I don't think it was user-friendly enough for that.

  <img width="403" alt="Schermafbeelding 2020-09-18 om 09 41 44" src="proxy.php?url=https://user-images.githubusercontent.com/10217/93574129-52ef9680-f998-11ea-9a6f-31144f66d3bf.png">

  This PR makes a few simple improvements so that new users don't have to think too much:

  <img width="369" alt="Schermafbeelding 2020-10-15 om 16 45 22" src="proxy.php?url=https://user-images.githubusercontent.com/10217/96145959-0c914700-0f06-11eb-9526-cf447d841d7a.png">

  It's lightly inspired by #77. It would be better if those changes made it into the upcoming release, but this PR is a good start imo.

  * wallet encryption is no longer checked by default, because such a change in the default needs a separate discussion (fwiw, I suspect it increases the number of users losing access to coins)
  * watch-only and descriptor wallet stuff is moved to advanced, so new users know they can safely ignore these check boxes
  * bonus: when you click on "disable private keys" it disables encrypt wallet and checks blank wallet
  * label changes: see screenshot
  * tooltip changes: see code diff

  Note that a blank wallet name isn't allowed in the dialog; I haven't addressed that.

  _Update 2020-10-30_, dropped the new strings for now:
  <img width="450" alt="Schermafbeelding 2020-10-30 om 11 26 55" src="proxy.php?url=https://user-images.githubusercontent.com/10217/97694591-1b99fc80-1aa3-11eb-8b85-e19f1ad5add4.png">

ACKs for top commit:
  fjahr:
    Tested ACK ac64cec
  jonatack:
    re-ACK ac64cec, per `git diff d393708 ac64cec` only change since my last review is improving the placeholder from "MyWallet" to "Wallet" and dropping the last commit. Tested creating a dozen wallets in signet with different combinations of options and then verifying/comparing their characteristics in the console with getwalletinfo. My remaining caveats are (1) the need for less user surprise by either (a) improving the user info or (b) with less auto-(un)selecting as mentioned in bitcoin-core/gui#96 (comment) and (2) I prefer the "Encrypt private keys" and "Watch-only" wording and descriptions below over the current ones; hopefully these can be addressed in a follow-up.
  hebasto:
    re-ACK ac64cec
  ryanofsky:
    Code review ACK ac64cec. Only changes since last review are tweaking placeholder text and dropping "allow nameless" commit

Tree-SHA512: a25f84eb66ee4f99af441d73e33928df9d9cf592177398ef48f0037f5913699e47a162cf1301c83b34501546d43ff4ae12607fd078c5c03b92f573bf7604a9f2