Added zlib sources for Qt5 compilation.
Ported BuildingEd window-shutter-tile stuff from TileZed.
BuildingEd: Added "dormer" roof objects.  Added half-tile edges and corners.

Slopes and corners could only be whole tiles high, now they can be created
in 1/2-tile increments.
Fixed MainWindow::writeSettings() calculation of the scene position.
Submap tiles outside a cell or adjacent map's bounds are not displayed.

When a building is placed outside a cell map, its tiles are chopped off by
WorldEd when generating binary .lot files.  This change allows the user to
see where that will happen.
MapComposite::addMap() calls ensureMaxLevels() on all ancestors.

Noticed that Lots loaded into adjacent maps weren't updating the maxlevel
of the root map.
Added zlib1.dll to dist.tcl.
Copied ObjectLabelItem fix from TileZed.
Copied MapComposite tool-tiles stuff from TileZed.
Copied building stuff from TileZed.
Ported CompositeLayerGroup::setToolNoBlend stuff from TileZed.
HeightMapView: load all Lots, render all levels.
Fixed MapBuildings not finding rooms on the highest level.
SubMapTool: "Open in TileZed" works for the cell's map.