Enlarge texts and fit the other elements

Basically set text size to 18sp and change layouts
along with the new design.

- Add custom list item xml for Wi-Fi security field
  rename existing "custom_list_item.xml" to appropriate
  name so that we won't be confused with their naming.
- Use the custom xml just in SetupWizard.

Bug: 3364731
Change-Id: I014903277a03c359ea193dd0f0a37c84ade19fa1