Add plot_spectum in misc/utils.py: saves spectra as cascade to file
Modify utils.py. Add mosaic style plot.
Modify utils.py: add heatmap style plotting of spectra
Modify utils.py, plot_spectra function. Remove multiple_plots variable, add multiple_plots style. Move cascade plot to own subplot function.
Modify utils.py: moved heatmap plot to seperate function
Modify utils.py: add x- and y-axis labels. Scale y-axis by the navigation axis in spectra.
Modify utils.py: move mosaic plot to own function
utils.py: removed ipdb import
Add possibility to plot single spectrums with plot_spectra
Remove incorrect documentation in plot_spectra
Merge branch 'master' into save_to_figure
Add way to set plot color for utils.plot_spectra
Fix bug in utils.plot_spectra
Add way to reverse plotting direction in plot_spectra

More specifically, reverse the navigation axis in cascade style plotting
Merge branch 'master' into save_to_figure

Conflicts:
	hyperspy/misc/utils.py
	hyperspy/signal.py
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)
BUG-FIX: the threshold argument of estimate_thickness was not mandatory