Boxing & unboxing is the process of converting a primitive value into an object oriented wrapper class (boxing), or converting a value from an object oriented wrapper class back to the primitive value (unboxing).
The Old Dalaran will stay in Northrend, so yes, mages are going to have 2 portals to dalaran (one to Northrend and one to the Broken Isles)
Sligo (Sligeach in Irish, meaning shelly place) is the principal town in County Sligo in Northwest Ireland & Lakelands. It is the largest urban area in this region, and the second largest in the province (after Galway).