Board on touch screen: scroll vs. drag&drop

When scrolling on touch screen I often grab issue instead. And when trying to grab issue I scroll.

Issues should have relatively small and visible handle (two lines or six/eight dots) on only which drag would work. Small draggable area would minimize accidental drags and would make obvious that there is drag&drop functionality and where to drag.

This also solves problems with selection, issue gitlab-ce#22545, because handle can have selection disabled without introducing usability problems.

This came out from discussion under issue gitlab-ce#21219.