Kickoff: Refactor and tweak design

Changes:

- Now uses implicit content size to set the size of the plasmoid, which
fixes translated string elision issues.
- Much simpler code. This is a red patch.
- Reduced RAM usage. Pages that are not in use are unloaded. The models
aren't unloaded, so it shouldn't negatively affect performance in other
ways.
- Vertical movement and opacity animation when switching from normal
page to search view.
- Single horizontal movement and opacity animation when switching from
applications page to places page.
- Opacity animation when switching from favorites grid to apps list.
- KickoffListView and KickoffGridView now support PageUp, PageDown,
Home, End, Ctrl+Home and Ctrl+End shortcuts like lists and grids do on
the web. See https://www.w3.org/TR/wai-aria-practices-1.2/#grid
- KickoffListView/KickoffGridView keyboard navigation disables hovering
to change current item for 100ms. It's meant to filter out accidental
mouse movement while using the arrow keys to navigate.
- Add Ctrl+F shortcut to focus search bar
- Focus the next item down when pressing down while the search bar is
focused instead of focusing the 1st item. The old kickoff did this and
made it faster to select and activate items.
- Hovering near the bottom/top of a view no longer rapidly selects a
series of new items lower down/higher up that are not yet visible.
- Single letter section headers are now horizontally center aligned with
icons.
- Scroll to switch tabs.
- Added pin button to keep the launcher open.
- Show tooltips for list/grid items that have elided text.
- Padding and spacing are more uniform.
- List items have better vertical pixel alignment.
- Fixed pixel alignment of arrows in sidebar category items
- Sidebar list items line up with main content area list items and
section headers
- Labels in grid items now have consistent vertical positions.
- Fixed error in tools.js with favoriteModel.enabled

BUG: 433103
BUG: 432270
BUG: 439140
BUG: 434736
BUG: 431913
BUG: 433146
BUG: 433241
BUG: 408313

FIXED-IN: 5.23