Set the amount of theta levels plotted in configuration.py

Currently, the amount of displayed plots (from 1 to 10) can be set in dashboard.py function. The default option is 2.

`
def plot_diagnostics(float_dir, float_name, config, levels=2)
`

Maybe instead of going inside this function and looking for the line where to set the number of displayed theta levels, it would be worth to have that setup in the configuration.py ?
