Implement more sensible line smoothing algorithms

ecerulm

Currently the line charts have the options Line > Smoothing that produces some artifacts (loops, X values with multiple Y values, etc)

It would be nice to have regular spline smoothing , etc, so that we can get rid of these artifacts

For reference the dataset that produces the artifacts

2013-01-02 1

2013-01-03 2

2013-01-01 1

2014-01-01 2

2014-11-14 1

2014-11-25 19

2015-10-22 1

2016-01-15 4

2016-09-04 1