kcms/baloo: modernize style

• Use ScrollViewKCM as the base element and move the non-view UI elements to the view header, so the KCM can't ever be in a situation where it has two scrollbars
• Put global-scope "pause/resume indexing" action in the header
• Move status text into the relevant part of the controls layout,where its positioning won't seem so random
• Make file path in the status text label selectable
• Use a FormLayout for the main controls
• Flatten list item UI elements and adopt alternating background style so they're more visually connected with their text
• Move footer actions to a fancy custom Kirigami-style ListView header to avoid the "two stacked rows of buttons" effect. If we like this UI element, we can make a generic component out of it and use it in other KCMs as well
• Tweak wordings

BUG: 469902 FIXED-IN: 6.0

@teams/vdg