Problems using PyQt5/PySide2 with the Mayavi app

When running the `mayavi2` application from the latest version of Mayavi on Python 3.6.x with PyQt5 (5.10.x) or PySide2 (5.11.1x), I run into some issues.

1. When closing the app, I get the following error:
```
Traceback (most recent call last):
File "ETS/pyface/build/lib/pyface/ui/qt4/workbench/split_tab_widget.py", line 305, in _focus_changed
self.focus_changed.emit(old, new)
TypeError: SplitTabWidget.focus_changed[QWidget, QWidget].emit(): argument 1 has unexpected type 'QObject'
Abort trap: 6
```
This is fixed with a simple `try/catch` block which seems rather hacky so am not sending a PR for that.

2. When the app starts up (after fixing the issue above or otherwise), the size of the TVTK scene on the app is tiny as shown. This doesn't seem like a retina display issue as the size is a fixed small size. No matter how I resize the window, it goes back to a tiny size when re-opened. Note that this does not happen if I remove all the other panels and just leave the editor area enabled.