Omit properties from export

Nobody has claimed this yet.

**Is your feature request related to a problem? Please describe.**
When I'm exporting to a tmj/tmx file, the json is full of useless information, which the engine ignores

**Describe the solution you'd like**
a toggle near every property, which is stored in the project file, this toggle is on by default, toggling it off, makes it so that property is ommited from the exported file (.tmx/.tmj)

Some properties like the background color have a "Not Set" state, which has the same effect, this would not work for some properties like Fill Mode, which tiled needs to render the map, but my engine already knows about, so useless information for the engine, useful for tiled, it needs to be set.

**Describe alternatives you've considered**
- Simply ignore the properties, not ideal, the file is polluted with useless information
- Post process the file, what I do, but again, I'm still exporting and then removing the information, not ideal

Since there are workarounds, this is low priority, I just wanted to point out the "not ideal" state of the matter.

The issue does not name specific files or tests. Start by locating the TMJ/TMX export and property-serialization paths, then determine how per-property preferences would be stored and applied; done means disabled properties are omitted while required export properties remain present.

Written by the indexing model from the issue text.