CardView: rework the drag'n'drop functionality.

 * simplified SwipeArea and SlidingItemArea
 * use a SwipeableCard based on ListView to swipe out the cards; this enables us to use a MouseArea on top of tag to drive the drag
 * the drag is now started with a simple long press, no need to release the mouse button to begin the drag
 * Use VisualDataModel components for the groups and for the cards to have a more flexible way to handle them in the view
 * Use a PathView for the group of cards instead of a Repeater, to be able to better control the way the cards are positioned
 * The MouseArea for driving Drag'n'Drop is place in the CardWindowWrapper, as this component never gets deleted when a delegate disappears
 * When the drag begins, the card is reparented to a top-level item which also contains all the Drop logic
 * It is possible to drop the card anywhere in a group of cards, or between groups.
 * By dragging a card of the sides of the screen, the list of cards is scrolled automatically.

Sometimes the drag'n'drop bugs, and the result can be a crash of luna-next. This is being worked on.

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
CardView: fixes for drag'n'drop.
 * reverted to a Repeater for card stack, as the PathView always loops on the path
 * avoid using "move" on VisualDataModel groups, as it is bugged in some cases. Prefer using remove+insert instead.
 * reduce the debug logs

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Cardview: fix remaining known bugs and polish the UI a bit

 * abandon unresolve delegates usage, which doesn't work well with a Repeater view.
 * simplify the anchoring condition (now it simply depends on Drag.active)
 * change the ordering of cards to have all card in a group on same z value so that childAt works well
 * remove useless "temporary item resolving"
 * introduce a little animation for angle and translation
 * fix bugs where artefacts appeared in certain drag situations

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Merge pull request #128 from webOS-ports/tofe/stackedcards

Tofe/stackedcards