Building pyside egg fails (Travis CI)

[jvkersch]

The Pyside2 and shiboken2 repositories are gone (https://github.com/pyside/pyside2) but we still rely on them to build a pyside egg.

This came up in #360

[corranwebster]

There is a similar problem in Enable. The fix is to switch to an EDM-based travis/appveyor script - TraitsUI has the current template for doing this.

[jvkersch]

Fixed in #365