Implement CLI version of s.remove_background

Only supports powerlaw and gaussian component, and only tested on
line-scans.
Only use the estimate_parameters function in the components. It should
rather do a full fitting-proceduce.
Add progressbar to remove_background_cli. GUI version use CLI function
Merge branch 'master' into remove_background_cli
Avoid numpy deprecation warning due to unsafe inplace operation in remove_background by changing the dtype of the background data. This solution has the extra benefit of not modifying the original dtype of the signal.
Incorporate _estimate_component_parameters in _remove_background_cli.
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
Merge branch 'master' into remove_background_cli
Merge branch 'master' into remove_background_cli
Docs improvements
Enable float/index axis indexing and None (to mean beginning or end of axis) in estimate_parameters. Also some small corrections to the test
Merge pull request #102 from hyperspy/remove_background_cli

Remove background cli