Collecting new/improved stuff in 5.1 for promo

[Eike Hein]

Folder:
- Significantly improved performance and memory usage in desktop mode.
- Faster, more responsive DND operations.
- Greatly expanded context menus.
- Support for the 'associated application' system is back.
- Keyboard nav improvements (support for Home and End keys, etc.).
- Spatial keyboard navigation (arrow keys, etc.) for unsorted views.
- Tooltips can be disabled.
- Icon size can be changed (disabled it shortly before 5.0 due to a bug).
- Better guard against corrupt config.
- Many bug fixes (a few bigger ones: graphical glitches with DND on some 
drivers addressed, sort by size was broken, anchored range selections on 
unsorted views misbehaved, drag-onto-to-launch for view-internal DND 
crashed didn't work, ...).
- Some platform fixes that show up here the first time, e.g. the view 
context menu now works when Folder is a panel popup.

Application Menu (Kicker):

- Basic support for editing menu entries right from the context menu 
(name, icon, command, etc.).
- Per-instance hiding of menu items.
- Basic integration with Muon Discover / package managers via 
PackageKit-Qt (you can jump into them via the context menu).
- Support for screen readers and other a11y software.
- Various bug fixes (a few bigger ones: improved positioning, "Add to 
Panel" with multiple applet instances in different panels could pick the 
wrong panel, initial keyboard focus when invoked via shortcut wasn't on 
the search field, ...).

Task Managers:
- Icons-only Task Manager is back.
- Improved lifecycle behavior for launchers and startup notifications 
(clean handoffs/replacing, less visually messy co-existence).
- More reliable identity mapping between startup notifications and 
launchers and windows.


Cheers,
Eike