Some discussion appeared about the fact the multi select was changing
height when pill were selected, making this input having a bigger
height than others making it looks weird in a form comparing to the
others. Modifying the padding and font size make the input keep the
same height.
See #114
Adding this new variant makes necessary to reorganize the files to keep
a clear separations of concerns. As of now Select/index.tsx is just an
entrypoint to render either the mono or multi variant of the select.
We do this in order to have homogenous border accross the entire
library, before we had DataGrid with 1px border and inputs with 2px
borders, which was not really nice to the eye.
