How do I control which NPCs live where?

An exciting new feature is described in the 1.1 patch notes:

• There is a new NPC housing interface that can be used to assign living areas to NPC’s. This interface will also tell you if a room is missing any requirements.

How can this interface be accessed?

Solution 1:

You can access this interface from the inventory menu. Near the PVP controls, just above the equipment grid, there is a small house. When you click it, you'll toggle the equipment to the housing interface.

You'll then be able to use the different NPCs faces to assign them a room, or the question mark to check if a room is able to house a NPC.