[Clock] Add world city is often triggered accidentally when swiping up

The main clock page shows at most 2 world cities after which the cities are hidden. To see the rest of the world cities, the user will have to scroll up. After viewing the world cities, when scrolling down quickly, the add world city button is often triggered accidentally. This should be avoided by stopping at the app edge.

There are 2 actions associated to this bug,

Flick: Action where the user swipes up/down and lets go. At the moment when the user lets go, the page is already scrolling
Drag: Action where the user drags the page up/down without letting go.

We want the add world city action to be shown only when the user is dragging the page down and not when flicking it down. That's the distinction that needs to be made.

Note: When there are less than 3 cities, a flick is equivalent to a drag since when the user flicks the page long enough, he is already at the app edge. In these cases, nothing can be done.