KPageView: Adapt margins when the view is searchable

Tweak a bit the margins for the search field and the title widget
to get a better overall visual alignment.

In the search field:
  - Remove completely the right margin, so it looks aligned with the
    selection list
  - Remove 2px on the bottom to account for the separator height
  - Remove 2px on the left to make the margins visually similar

In the title widget (from a 4px default):
  - Add 1px on the left to account for the vertical separator
    This aligns the title with the text on the content
  - Remove 2px on the bottom to account for the separator height