* updated DropdownButton props
* refactoring in progress
* working but layout is wrong
* fixed bug
* wip on ColumnHeadWithDropdown
* fix bug
* fix bug
* remove unused styled component
* fix z-index bug
* add an optional argument to DropdownMenu to control the offset of the menu
* add an optional argument to DropdownMenu to control the offset of the menu
* modify files after PR comments
* clean the way the offset is handled
* fix lint
