Scrollbar issues inside mn-select component

The scrollbar inside mn-select component has some issues:

• it is not obvious for the user that the dropdown menu is scrollable; the user needs to start scrolling the menu before the scrollbar appears on the right; I think we should make the scrollbar should be visible when the user opens he dropdown menu.
• if a select component has both a scrollbar and a search input, the scrollable content also contains the search input, leading to an unpleasant UI; the scrollbar should scroll only the options from the dropdown menu.