Fix label in NEBAnalysis (#4473)

* clean up type and docs

* remove non-existent interpolation_order arg

* clean up comment for arg `spline_options`

* clean up doc more

* deprecate `spline_options` with a more understandable zero_slope_saddle flag

* exact match first for glob

* completely deprecate spline_options

* completely deprecate spline_options

* more doc and type cleanup

* a -> an NEB

* fix relative energy

* fix test

Author: DanielYang59