A few changes concerning wxGTK.

For one, I added a new member gs_window for future use.
The member is "display" which represents our connection to X11.
Ideally, we should use this specific connection to deal with our Window.
For now, it's disabled. Read comment for more information.

Secondly, wxGTK apparently doesn't map our window in some cases.
This causes the window ID passed to be bad and will stop (or segfault)
our program. This might be related to the first commit above.

For now, all this commit does is realize the window manually.

libobs/graphics/graphics.h

@@ -415,7 +415,9 @@ struct gs_window {
 #elif defined(__APPLE__)
 	__unsafe_unretained id  view;
 #elif defined(__linux__)
+	/* I'm not sure how portable defining id to uint32_t is. */
 	uint32_t id;
+	void* display;
 #endif
 };