Reorganize and clean up lock screen section

- Move the option for enabling widgets to the top of the widgets header,
  as it 1) is the most important option in that section, 2) is most
  likely going to be what the user is looking for first and 3) is a
  dependency for most of the other settings in that header.

- Use the simple and intuitive AOSP "enable widgets" title for enabling
  widgets instead of the verbose "widget pager" term.

- Shorten and simplify overly long, hard to parse space-hogging
  summaries.

- Move "slider shortcuts" out of the widgets section.

- Hide "maximize widgets" option on low ram devices

Change-Id: Iac1b55a6b976c5645ca7f46e7fdf0821396e1100