signal.remove_background: add components and improve docstring

Add Offset and Polynomial components
Expand docstring and add example
Add test for signal.remove_background

Only tests with the gaussian background type
Add test for signal.integrate_in_range.

GUI function now opens the integrated spectrum.
Add uint <-> RGB conversion to change_dtype
Add RGB tests
Remove unused mpl_traits_editor
Make Hyperspy work with Qt and PySide and set Qt as the default backend
Make hyperspy work without X server
Enable running hyperpsy using the inline IPython pylab backend. Also enable choosing the toolkit and pylab_online in preferences
BUG-FIX: the msa files were not being added to the distribution
Correct version, back to dev
Merge branch 'master' into ENH_toolkit_choice
BUG-FIX: hyperspy/tests/drawing was wrongly placed in setup.py
Merge branch 'master' into ENH_toolkit_choice
BUG-FIX: IPython version < 1.0 did not work due when choosing gui=qt4
Also check if sip is installed
Update api doc
Merge branch 'master' into ENH_toolkit_choice
Update api doc
Improve the way in which we check IPython version and import the interactive namespace