Allow opening arbitrary split-view configurations from the command-line using the shell integration.
Example: "open! file1 / [ file2 - file3 ]" creates a horizontal split, and splits the right half vertically.
By the way, make the view-reconstruction code more robust, so it doesn't screw up on specific changes to
the area indices. This should also fix some possible bugs/crashes in conjunction with working-sets containing many split-views.