Allow Panel to reuse Dolphin main Context menu.
Move a lot of actions handling from DolphinMainWindow and DolphinView.
In the process expose more slots.
Pass the KItemListSelectionManager and KFileItemListView of the foldersPanel around to have the selection accessible in DolphinMainWindow and DolphinViewActionHandler.
BUG: 270360
BUG: 406028
BUG: 420587
FIXED-IN: 20.08