Update work challenge to align with material next

Summary:
* Update title, subtitle, description and icon
* Update layout for entering credentials

Follow-up:
* There are still some UI componenets which don't
  fully align with material next. A larger
  change will need to be made to fix this, which
  we will aim to do in Android T.
* This includes the status bar and nav bar appearance
  and the password entry text field.

Pattern:
* Settings (WAI): https://screenshot.googleplex.com/BiQYeWSrkxL6iRW
* Work Challenge (after changes): https://screenshot.googleplex.com/7ThwqMpbHu8yLWg

Password/PIN:
* Settings (WAI): https://screenshot.googleplex.com/9zUMGgYBvyhYdBa
* Work Challenge (after changes): https://screenshot.googleplex.com/46SVNAzkWesyi8M

Bug: 191948779
Test: manual testing using TestDPC
Change-Id: I6cca39d447e37310c287d1a0eb0468565e9fcd37