Fixed bug with disappearing on bounce cell (second from the last one in collection)

[Skogetroll]

In current state viewController's view is being removed in didEndDisplaying and added only cellForItemAt. For the cell next to last ones (or to be more correct ones on the edge of the collection: first and last one) on bounce didEndDisplaying happened, so view was removed, but cell had no need be created, so cell ended up without view in it.

This fix just add view of viewController on willDisplay, iff it's not already subview of the cell. So even cell loses subview on didEndDisplaying during bounce, it gets it back before displaying.

Also, @objc added to didTapGesture because #selector() was demanding it.