Change kwarg stitle to scalar_bar_args

[AlexanderJuestel]

As shown in #636, we need to change the stitle kwarg to scalar_bar_args as it will be deprecated by pyvista soon. An attempt to fix this is made in 89a8d5f where the scalar_bar_options are saved as new dict called sargs and the title of the plot is added as new value and new key. The keyword stitle was removed from add_mesh and the new dict was passed to scalar_bar_args

https://github.com/cgre-aachen/gempy/blob/2a76ec8bbb27b2e1a9d4c8acb7455fb2a577934d/gempy/plot/vista.py#L669-L694