Keep splitted view when coming back from a maximized view

[QDoussot]

Old behavior

• Open a splitted view like ("Main + Diff" or "Status + diff" for example)
• Then open a new maximized window like help
• Quitting the maximized view does not bring back the splitted view but only the top view ("Main or "Status" for example)

  New behavior

• Open a splitted view like ("Main + Diff" or "Status + diff" for example)
• Then open a new maximized window like help
• Quitting the maximized view does bring back the splitted view ("Main + Diff" or "Status + diff" for example)

Example:

From Main view
 :enter      -> Main view | Status view
 :view-help  -> Help view
 :view-close -> Main view               (old behavior) 
 :view-close -> Main view | Status view (new behavior) 

Enable requested behaviors in https://github.com/jonas/tig/issues/336