Code is currently Qt-specific

[corranwebster]

Even if there is no plan to write a WxPython version of qt_message_router any time soon, it might make sense to put some of the machinery in place to allow it.

The simplest approach for now would be to check that the value of ETSConfig.toolkit is either qt4 or qt before importing qt_message_router and throw a reasonable exception if not.

A slightly better approach would be to have an entry point for the message router keyed off the value of ETSConfig.toolkit which would at least allow 3rd parties to contribute their own message router.

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EDIT [mdickinson, 2018-08-04; adding subtasks]

Subtasks:

• add entry-point-based mechanism for getting the router: Allow message router to be pluggable, via entry-points. #70
• add a wx message router: [POC] Feature: support for wxpython #72
• add tests for the wx message router (possibly not easy): [POC] Feature: support for wxpython #72
• make all tests run on wx: [POC] Feature: support for wxpython #72
• include wx in CI test runs: [POC] Feature: support for wxpython #72
• make progress example work on wx

[mdickinson]

It doesn't look too hard to write a wxPython version of the message router; the challenge is testing it properly without the GuiTestAssistant (which currently only exists for qt).

[mdickinson]

Experimental (but working, and unit-tested) wx support is in #72. That PR probably needs to be broken up into several pieces.

[mdickinson]

For testing on wxPython, see enthought/pyface#266.

[mdickinson]

Largely fixed in #246. There's an outstanding issue for making the examples work under wx: #253.