Move functions from misc/utils to drawing/utils and import plot_spectra in hyperspy/utils.py
In heatmap disable interpolation and cmap choice (this will be chosen in Hyperspy preferences)
Small style corrections
Remove option to save plots to file as this is an unexpected behaviour for a function called plot_spectra and it can be easily done in a more pythonic way e.g. plot_spectra(...).savefig(example.png)