Update jquery ui to latest git version and apply local modification.
Deactivate doomline (has strange behavior with drag and drop)
Refactorized backlog drag and drop.

Make it work like other drag and drop implementations
found on taiga (taskboard and kanban) with exception of
revert animation.
Merge pull request #1 from taigaio/backlog-sortable-refactor

Backlog sortable refactor