Add options to disable certain features

[bjorn]

It happens quite often that you need to avoid using certain features, either because they are unsupported by your game or for any other reason. This can be quite tricky, for example it's easy to accidentally flip some tiles or to rotate some objects.

In addition, some features add UI elements which take up space. If a project does not use object templates, then the Template Editor view and the Insert Template tools could be hidden entirely. If rotation and scaling are disabled, the related properties can be hidden and no handles should be shown when using the Select Objects tool.

Now that Tiled supports projects (#1665), we have a good place to add a kind of "feature flags".

List of suggested features that could be toggled

• Tile flipping (hopefully one setting for all flipping bits would suffice).
• Object rotation
• Tile object resizing
• Tile Collision Editor
• Terrain Tool and related view in Tile Editor
• Wang Tool and related view in Tile Editor
• Object Templates
• Each layer type (tile layer, object layer, image layer, group layer)
• ... (please comment if I'm missing anything you'd like to see!)

Of course, one question is what to do when an opened file already used any of the features that may be turned off. At the least, no data loss or crashes should be expected in this case, but you may not be able to edit the data covered by the disabled features.