Override video mode list in Team Arena UI

Override the video mode list in the Team Arena data files with detected
modes from SDL like in ioquake3's Q3 UI. Add the aspect ratio to the
end of the video resolution (i.e., "640x480 (4:3)"). Add the current
(custom) video mode to the list.

Before when using a custom resolution in the menu you could not change
the video mode using the mouse because the resolution text was blank.
Now custom video resolution is displayed and can be clicked.

code/ui/ui_shared.h

@@ -203,6 +203,7 @@ typedef struct multiDef_s {
 	float cvarValue[MAX_MULTI_CVARS];
 	int count;
 	qboolean strDef;
+	qboolean videoMode;
 } multiDef_t;
 
 typedef struct modelDef_s {