Added "Open in TileZed" to WorldCellTool and SubMapTool context menus.

Mash wanted a way to open maps in TileZed from WorldEd.
Fixed crash with resizing a world when lot images aren't displayed.
MapManager creates RoomDef map objects after loading a building.

LotFilesManager needs the RoomDef objects for maps that were created from
building .tbx files.
Rooms in a .lotheader have a list of rectangles making up each room.

The .lotheader file already had a list of buildings, and for each building
a list of room rectangles making up rooms in that building.  Every room
rectangle was made into a separate room, which wasn't correct for non-rectangular
rooms.

Now, each room has its own list of one or more adjacent room rectangles
that make up that room.  Adjacent rectangles are merged only when the names
of the rectangles contain a hash # character and are the same.
Fixed a crash when reloading a map.

MapComposite::recreate() calls addMap() which calls ensureMaxLevels() which
generates the layerGroupAdded() signal.  There was a bug with mMaxLevel not
being reset to zero in recreate() which caused ensureMaxLevels() to add null
entries to mLayerGroups, crashing out in CellScene::handlePendingUpdates().