Fixed plot_3d colorbar's incorrect range
Fixed plot_3d colorbar's incorrect range

- changed format_ax() function in plotting.py to check if plotting a 3d plot or not before returning a fig and ax object
    - done by adding an additional argument `is3d` which is False by default
- found bug in format_ax() where you cannot compare the type of a ax object to the matplotlib subplot type
    - results in an error if you attempt to pass an existing axis object to a plot function
    - left unresolved for now

PlasmaControl/DESC,PlasmaControl/DESC