V2.3.0: removal of `customizable_properties`

In this new release of MATRX a much hackled feature has been removed: the customizable_properties. Before, you had to specify any property of any object you wanted to be able to change in an action, such as the image of a door, or the visibility of a block.
This feature was not (voluntarily) used, and only confusing. As such, it has been removed.

New features

• Removed the need for specifying customizable_properties. From now on any property can be changed with your_object.change_property() from an action without specifying it in customizable_properties! Using customizable_properties gives a deprecated warning. #321 #212