BUG_FIX: smooth_lowess was broken due to wrong import.
Automatic style corrections courtesy of autopep8.
lowess: add meaningful ValueError exceptions.
Automatic style corrections courtesy of autopep8.
Improve SmoothingLowess UI by using Range instead of Int
Remove broken numerical differention from smooth_lowess and smooth_tv.
Replace in-house savitzky-golay with scipy one.
Replace in-house lowess smoothing with statsmodels one.
Add +/- buttoms to savitzky-golay UI.

Also decrease code duplication and remove differential order from
`smooth_lowess`.
smooth_lowess uses Signal.map.
split processing from UI in smooth_tv and smooth_savitzky_golay
Merge branch 'ropeproject_gitignore' into BUG_FIX_smooth_lowess
Merge branch '0.7.2' into BUG_FIX_smooth_lowess
Add smoothing tests
Fix estimate_elastic_scattering_threshold that was broken due to savgol arg name change.
Add  argument to progress bar
Add  option to Preferences
Add  method to DummyProgressBar.
Make Preferences.show_progressbar the default for all progressbars.
autopep8 corrections