[#73183568] dropdowns +  [#73270894]buttons-dropdowns

in dropdowns

- [x] last dropdowns pattern (which uses [plugin](http://davidstutz.github.io/bootstrap-multiselect/))
 - this pattern doesn't have the same appearance as those in design comp.
is it possible to define magic number like https://github.com/gengo/style-guide/blob/master/scss/_variables.scss#L494 ?
but I'm not sure this is efficient to define variables like that.

@marexandre @vwxyz do we need to talk about this ?