 Correct link shortcut so that it inserts, selects text or moves cursor properly
 Correct link shortcut so that it inserts, selects text or moves cursor properly

 Closes #2614
 - Determine proper place for selection, or simply move the cursor.
 - When no text is selected insert link markdown and move cursor to a into the [].
 - When text is selected insert link markdown and move selection to http:// so URL can be pasted.

TryGhost/Ghost,TryGhost/Ghost,TryGhost/Ghost