View accepts FirstResponder (for key_press_events)

In macos backend, [View keyDown:] (connects Cocoa event loop to mpl
key_press_events) was not being called because View did not accept being
first responder.

Author: mrterry

src/_macosx.m

@@ -419,6 +419,7 @@ - (const char*)convertKeyEvent:(NSEvent*)event;
 - (void)keyDown:(NSEvent*)event;
 - (void)keyUp:(NSEvent*)event;
 - (void)scrollWheel:(NSEvent *)event;
+- (BOOL)acceptsFirstResponder;
 //- (void)flagsChanged:(NSEvent*)event;
 @end
 
@@ -5660,6 +5661,11 @@ - (void)scrollWheel:(NSEvent*)event
     PyGILState_Release(gstate);
 }
 
+- (BOOL)acceptsFirstResponder
+{ 
+    return YES;
+}
+
 /* This is all wrong. Address of pointer is being passed instead of pointer, keynames don't
    match up with what the front-end and does the front-end even handle modifier keys by themselves?