Ability to re-arrange tilesets in tileset window is broken.

In older versions of Tiled, you were able to re-arrange the tilesets in Tiled's tileset window by click-n-dragging on the the tileset's tab. This also restructured the "firstgid" value in the TMX file, and reorganized the map's data accordingly.

As of 1.0.0 and 1.0.1, this feature no longer works. The only way to re-arrange tilesets now is to delete the tileset, and re-add it at the end of the list. This obviously also breaks your maps, and will remove any tile data on the map.

To verify that this feature did work in past versions, I re-downloaded version 0.18.2 and recorded this GIF:

This feature is vital to me, because my game engine expects certain tilesets to be loaded in a certain order (for example: collision_tileset > level_specific_tilesets > tilesets_only_used_wihle_level_editing)

Reproduce the problem in the tileset window in Tiled 1.0.0 or 1.0.1, then compare it with the working behavior shown for version 0.18.2. Done means dragging a tileset tab reorders the tilesets, updates firstgid values, and preserves the map's tile data.