Add basic drag handlers and drag CSS styles for channel-item.
Part of #79
Add ease effect when drag start.
Part of #79
Swap channel items content when dragging and dropping.
Part of #79
Refactor swap logic.
Part of #79
Minor. Increase opacity for draggable channel items.
Part of #79
Minor. Remove unnecessary self var.
Update channels position in channels collection to avoid wrong sort order on redraw.
Note: This needs code review from a core contributor.
Part of #79