Responsivness and single item options

Bug Fixes

• drag-drop: solved problems with inputs in gridster-item container
• drag-drop: bug fix with fast dragging item from outside

Features

• config: Gridster responsive behaviour
• config: different Gridster configuration for different breakpoints
• drag-drop: disabling/enabling moving item in gridster
• resize: disabling/enabling resizing item in gridster
• api: new change event on GridsterItem
• config: new GridsterItem options
• deps: update angular env to newest version
• demo: extend demo page
• config: shrink Gridster height to fit items