fix(move): remove drag support on shape remove
chore(selection): properly deal with hammerjs events

This commit ensures we unwrap hammerjs-events to access shiftKey /
srcElement in selection handling.

BREAKING CHANGE:

* selection has been refactored to use prototype, during this change the
method #getSelection as been changed to #get.
feat(move): decrease visible lag

This decreases the visible (and percived) lag during drag by

* performing less cloning
* performing less picking

during move events (that may occur often)
feat(overlays): hide overlays during viewbox change
feat(overlays): remove overlay if element got removed