Convert Modeldata to Dict

[zeryx]

This PR removes the user_data and system_data objects of ModelData, and instead converts the modelData object itself into a dictionary type! This dramatically simplifies interactions in load functions, and allows for easy use by algorithm developers to store data that can later be used at runtime, without having to create a separate object, or reference a special member or method.

Now if you want to export everything what was recorded in userspace, you simply need to call the .data() method, which returns a dict containing the key/value pairs stored.

[aslisabanci]

i like this simplification :) nothing stood out for me, so 👍