Cancel press if a drag is started
Run press-composer tests
Make buttons draggable

By not preventing default on pressStart. This was to prevent
scrolling of the webpage so that if the button is inside a
scroller it will scroll instead of the page. The preventDefault
has been replaced by preventing default on touchmove instead (if on
touch). On mouse this is not a problem.
Merge pull request #1096 from Stuk/press-dnd

Make press-composer/buttons work with native drag and drop