Add Flip toggle button to StoryItemOptions

[birbilis]

Version: 0.5.12

Should add a Flip toggle button to StoryItemOptions (and respective property to IStoryItem/TStoryItem).

When true it would mean that in non-Edit mode a double-click (double-tap) to a child StoryItem of the ActiveStoryItem, that child item would rotate the Z-order of its own children, by sending the top one to the bottom

That way can make flipping cards (with two children in them) or items with more/multiple visual choices by just having in them multiple children of the same size stack one above the other

It would be nice it the parent item could inherit the tag of its top child in that case (or effectively merge its tag list with its own tag list when such are supported) to be able to pick alternative choices when solving drills by moving card with correct face (choice) onto a target