Corrected some misspelled 'Exception()' in header.py

m_to_deg was not an existing function. Used obspy locations2degrees instead.

Added a header field for N-Np-Ns which changed depending on which type of plot is used. I used a decorator to append additional header information to the header class, which gets written on plot if present.
They will be present by default, but the decorator make it easy to remove if needed.

Added a new normalization based on median amplitude. Fixed issues with station_amplitude that was not working properly. Moved normalization logic (now based on precomputed list of amplitude factor instead of internal loop that compare dat and syn).

Changed the median normalization logic into a function, in order improve readability and reduce redundancy in the plot_waveforms1 and plot_waveforms2 functions.

Modified normalization list building logic. Previously, it would break on calls of 'station_amplitude' and 'trace_amplitude' due to previously added changes.

I reverted the pull request back to including only the median scaling (removing new header treatment and decorator function). The new header field will come in it's own PR.