Update naming conventions for settings object

[bzkrouse]

Update chart arguments to be consistent with naming conventions of other safety charts. Keep support of previous argument names until next major release. This includes the following changes:

id -> id_col
major -> major_col
minor -> minor_col
group -> group_col
placeholderFlag -> missingValues
totalCol -> showTotalCol
diffCol -> showDiffCol
prefTerms -> showPrefTerms

[jwildfire]

Probably just going to want to hold off on this until v4.0