Condition display of progressbar on a isCreatingAccount LiveData

Avoiding the mess with saving onSaveInstanceState, and the (in this
case) unwanted restoring of it upon back-button tap.

Closes #1919

Test instructions:

- Precondition: fresh install, setting up a new account
  - Testing specific bug fix:
    - Choose a name, tap next
    - Choose a password, tap next
      - Not testable on some devices which display "Create account" instead of "Next"
    - You are now on Background connections screen
    - Tap Back-button ◁
    - Ensure that password can be changed again
  - During setup process, rotate device and ensure that:
    - entered text is kept
    - progressbar is continuously displayed
2 jobs for 1919-password-fields-not-focusable in 9 minutes and 40 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Test
passed #7427
test

00:09:40

 
  Optional Tests
manual #7428
allowed to fail manual
manual_tests