WIP, basic implementation for event series emulation of: pointer_down -> pointer_move -> pointer_up.

Basic usage on LinearSelector.

LinearSelector todo:

• hover-on, hover off colors
• pointer down -> move -> up series
• middle click
• double click to activate keyboard arrow movement events
• check that keyboard arrow events move the selector w.r.t. step size
• sync with other selectors with and without modifiers

Should probably also set the linear selector to keep the hover-on color state when it is being moved, to prevent the flickering colors. Reset the color after "pointer_up"