[Suggestion] Allow custom entity graphic

[Geokureli]

Often I find myself wondering whether I should use decals to create my levels meaning the editor accurately shows what my level will look like in game but I can't apply properties to the objects, or use Entities, allowing me to give them properties but have a generic red box represent various graphics of different size.

Usually I end up making a few entities templates with the exact same properties and a different graphic, or I search for specific decals in-game by their filepath and change their values to hard coded ones. Neither one of these is a great solution.

Now that we have filepath value types I think it would be cool if there were a way to have a graphic override for entities. I suggest doing this using a similar graphic value type

• Graphic value types would show on the entity's property and template the same way as a filePath property.
• Allowed extension would be limited to image formats that Ogmo can handle.
• The Template view would have a "Use this graphic in the editor" checkbox. only one graphic value per entity can have this enabled
• On properties with that box checked, when the user selects a graphic path in the properties, Ogmo will display that graphic instead of the default graphic for the entity.
• Leaving this property empty shows the entity's default graphic, perhaps with a greyed out "default" in the field.
• (Optional) If a graphic property is not meant to override the editor graphic perhaps we can show that graphic, either in the properties window or through a "show" button that pops it up (maybe too much work for now)

Alternatively, we could have a checkbox here:

When enabled it adds a "Graphic Override" Property. but then we have to worry about naming collisions with existing properties.

I think this is a good opportunity for me to start contributing to this repo since it's just utilizing existing features, but I'd like to know your thoughts.