Added the new SW and NE corner sloped roof tiles.
Fixed the wrong tile offset for roof corners being used.
Mapped double-click event to single-click event for tools in the iso view.

The ortho view already did this.
Renamed BaseFloorEditor, FloorEditor, FloorView, BuildingTileModeScene, BuildingTileModeView.

BaseFloorEditor       => BuildingBaseScene
FloorEditor           => BuildingOrthoScene
FloorView             => BuildingOrthoView
BuildingTileModeScene => BuildingIsoScene
BuildingTileModeView  => BuildingIsoView
Renamed FloorEditor.cpp/.h to buildingorthoview.cpp/.h.
Renamed buildingtilemodeview.cpp/.h to buildingisoview.cpp/.h.
Renamed BuildingEditorWindow::roomEditor and ::mTileModeScene.
Removed unused code.
Added an assert that would have caught a bug.
Allow .tbx files to be used as Lots.
BuildingMap adds TilesetManager::missingTile() to maps.

If a building tile couldn't be found, the special "missing" tile is added
to the map representing the building.  In order to track whether a map has
any missing tilesets we need to add TilesetManager::mMissingTileset to the
building's map.

This was more important in WorldEd where the lot generator reports missing
tilesets.
Double-clicking or dragging a .tbx file to the main window opens it in BuildingEd.
Fixed missing category tiles all being placed under the "missing" header.
Use the same thumbnail image naming convention as WorldEd.
Fixed .tbx safe-saving breaking the FileSystemWatcher system.

When a .tbx file is saved, the original file is first renamed to *.bak then
the new file is written.  The QFileSystemWatcher class reports the renaming
of the original file being watched but then stops reporting any change to
the new file.
Ported some TileMetaInfoMgr meta-enum methods from WorldEd.