Setter takes a 'view', grabs the current cursor position, and dumps it into localStorage with a related key.

Getter takes a 'view', loads the related localStorage key, and *if* an editor instance is focused, sets the cursor position in it.  The CM instance must have focus on it already-- related code is in next commit.

When the component is mounted, it focuses the editor and the getter method to set the cursor.  It checks for a CM instance first, to avoid issues with properties editor.

When component is unmounted, it saves the cursor position.

When the view/editor changes (text to style etc), the current view cursor is saved, and the new view cursor is loaded.

…9/homebrewery into preserve-cursor-position

Add a 'beforeunload' event listener to watch for the user leaving the page so that the cursor position can be saved between page reloads.  For reliability, the setStoredCursorPosition method now returns null, which when run through the beforeunload listener triggers it, without opening a window prompt.

Just updating the old ref syntax to thew newer createRef syntax.