EHN: line_style option for plot_spectra
EHN: add legends
typos
EHN: improve yticks and ylabel

Change the yticks and ylabel to match as much as possible
plot() function.
EHN: documentations
Merge branch 'plot_spectra_more_options' into plot_spectra_xylabels
DOC: sub-title to title
DOC: udpate images

and some small changes in the doc
Merge branch 'plot_spectra_more_options' into plot_spectra_xylabels
EHN: 'overlap'
EHN: Default option in preferences

Create Plot option in preferences
EHN: tidy up preferences

Plot_on_load an pylab_inline in Plot
BUG: loop problem for mosaic

mosaic was not able to work two times in a row
DOC: no print of default from preferences
Merge pull request #142 from pburdet/plot_spectra_default_options

Plot spectra default options