[Feature-GUI] Implementing Evision.Wx

[cocoa-xu]

As mentioned in #103:

Even compiling OpenCV with highgui module, sometimes the Evision.HighGui.imshow function does not really work as expected (in evision): the window(s) it opened will not respond to any GUI events until calling Evision.HighGui.waitKey again.

To make it as good as one would expect it to be, like how it is in C++/Python, perhaps it would require one to invest a few weeks of time for it. But I'm focusing on other aspects of this library right now, also I'm hesitating to do it because I don't know if this would worth that amount time.

Also, as :wx has official support from Erlang, and it's well tested, and one can even build a relatively complex GUI app with :wx if they want.

This module will try to make itself easy to use. Meanwhile, the Evision.HighGui module will stay in the source code even after Evision.Wx is completed.

Here is a non-exhaustive list of desired/prospective functions in Evision.Wx. All of them, including the type and the number of their input arguments, are subject to changes in the future, or will not be implemented if the desired functionality is partially or wholly impossible to achieve in Erlang/Elixir with :wx.

• imshow/2. Equivalent of cv::imshow.
• destroyWindow/1. cv::destroyWindow.
• destroyAllWindows/0. cv::destroyAllWindows.
• namedWindow/2. cv::namedWindow.

Functions available in OpenCV's highgui module can be found here.

Any contributions or suggestions (either about Evision.Wx or Evision.HighGui) are more than welcomed - this also applies to the whole project. :)