Follow volcanoplot and pass settings object around instead of renaming columns in Scatterplot Module

[pburnsdata]

Originally I renamed the columns in the top level module and then used the new names in other functions/modules. However, I noticed volcanoplot just passes the settings object everywhere. It feels less readable to me, but it does clear need for global vars for cmd check and the rename did feel hacky....

This only covers implementation in the scatterplot module.

is follows example of volcanoplot and will reduce need for global vars in zzz.R