link bokeh scatter and lines in backfield plotting

[Swanson-Hysell]

We need to link the dots and lines in rmag.plot_mpms_dc():

like is done in plot_ac

[Swanson-Hysell]

This has been completed for plot_mpms_dc(), but still needs to be done for the backfield functions where the raw point and line isn't linked: https://pmagpy.github.io/RockmagPy-notebooks/hysteresis_backfield_notebooks/backfield_processing.html