Add editor split component (#198)

Add split and split divider component

src/components/common/split-divider/split-divider.tsx

@@ -0,0 +1,15 @@
+import React from 'react'
+import './split-divider.scss'
+
+export interface SplitDividerProps {
+  onGrab: () => void
+}
+
+export const SplitDivider: React.FC<SplitDividerProps> = ({ onGrab }) => {
+  return (
+    <div
+      onMouseDown={() => onGrab()}
+      onTouchStart={() => onGrab()}
+      className={'split-divider'}/>
+  )
+}