This will make it easier to ensure we are always using the appropriate
data type in the DataChanged signal since we won't need to hand pass
i32s around and instead define them once in the function get_role.
slide_model.rs activate function now properly tells of the data that
was changed so that ListViews that use it as a model will reset their
data properly on changes.
The important parts were to ensure we are using the right indexes for
top_left and bottom_right. Then also ensure the roles are correct, but
I think I had that already, just went with the implementation that
CXX-Qt used in their examples.
While the previous function technically worked, the connections
weren't setup properly. Also the row_count function wasn't running
because it requires a QModelIndex parameter. Added a simple count
function to make sure we know how many slides there are in QML.
This model, built in Rust, works in that functions are getting called
and the right pieces are mapped into the model. I've yet to connect
things up to see if QML is talking to the model just yet.
