Made it focus the new pane and added more modes.

* Ctrl+space, n, [-\]: open a new file in the new pane.
* Ctrl+space, c, [-\]: copy current view into new pane.

Also reorganized the way commands are called to be more general.
Add some error info.
Remove outdated comment.
Add keybindings for moving views.
Added open anything and open project keybindings.
Made delete pane actually work.
Added navigation commands.
Added the ability to split and copy or move the current view to the split.
Improved delete.

* Fixed typo that had it walk the wrong way to adjust sizes in some cases.
* Only delete an empty pane, otherwise act like close.
* Adjust views to the right pane number when closing.
Implemented resizing of panes with the keyboard.
Let you move splitters around for a while after starting.