Object Types should be moved to Map

Tiled have a global settings dialog with some properties like language, compress format, automapping and object types.

Tiled needs a Document properties, where we could have a dialog with settings of that file that would be introduced in the Map instance and saved to the file.

Like Object types, its nice to have global Object types and they can be loaded/saved wish is great!
But if you work with different projects at the same time its annoying to have to load the object types every time you change project.

Object types definition could be saved in the map itself, or be linked to a file with the types.

Start by reviewing the global settings dialog and the Map instance or map-file handling mentioned in the issue. Determine how document properties and object types are currently loaded and saved, then define what map-specific persistence and project switching should look like. Done means object types can be stored with or linked from a map without requiring repeated global loading.

Written by the indexing model from the issue text.