EHN calibration_on Copy the calibration and all metadata of a reference

Needed to calibrate INCA ripple
Merge branch 'axes_ui'
Merge branch 'master' of github.com:hyperspy/hyperspy
EHN: to_image and to_ spectrum modified

Possibility to choose the signal channel
Merge branch 'master' into ENH_spectrum_3D_dimension
Merge branch 'ENH_spectrum_3D_dimension' into NEW_edsSpectrum
EHN. corrected docstrings

better examples
Merge pull request #72 from pburdet/ENH_spectrum_3D_dimension

Fixes #70. EHN: to_image and to_ spectrum modified.
EHN background image spectrum for 2D

add manually in plot() a background
Merge branch 'ENH_background_for_plot' into NEW_edsSpectrum
EHN background image spectrum for 2D

add manually in plot() a background
Merge branch 'master' into NEW_edsSpectrum
Merge branch 'ENH_background_for_plot' into NEW_edsSpectrum

Conflicts:
	hyperspy/signal.py
EHN max and min for signal

create max and min similar to mean
Merge branch 'ENH_max_min' into NEW_edsSpectrum
Merge pull request #73 from pburdet/ENH_max_min

EHN max and min for signal
Correct small typos in docstring
Fixes #74
Fixes #75
Merge branch 'master' into NEW_edsSpectrum