Add additional actions to the file browser

o: open file in new tab
O: open file in current tab
i: open file in horizontal split
s: open file in vertical split

Any of the above can also be used to expand and collapse directories.
Rename VROutlineView to VRFileBrowserOutlineView
Remove VRMovementsAndActionsProtocol
Add status message view to file browser status bar
Add additional keyboard actions and feedback via the status bar
Use NSDeleteCharacter instead of NSBackspaceCharacter for deletion
Add actionIgnore to VRFileBrowserActionDelegate

actionIgnore should be called anytime a key is ignored. Keys are now
ignored instead of being passed to super keyDown: to provide
consistent behavior.
Only accept printable ascii characters in line editing mode

This is not a complete solution, but it's good enough for now.
Clear status message before processing keys in normal mode
Implement file browser menu actions
Trim whitespace from line editing string and ensure string is not empty
Clear status message when line editing ends
Implement search and n, N actions
Remove existing file if necessary when copying and moving

At this point the user has confirmed that clobber is okay
Fix endLineEditing updateStatusMessage ordering
Use shorter error message
actionReset if selection changes or file browser loses focus

- Set mode to normal
- Clear status message
Set _fileOutlineView.allowsEmptySelection = NO
Only allow add menu action if the file browser is empty
Expand directory when adding node