Log with category APPLICATION

All our logs should use APPLICATION category. The logs for other
categories are not printed by default under the "critical" level.

app/src/tinyxpm.c

@@ -69,7 +69,7 @@ SDL_Surface *read_xpm(char *xpm[]) {
     // parse image
     Uint32 *pixels = SDL_malloc(4 * width * height);
     if (!pixels) {
-        SDL_LogError(SDL_LOG_CATEGORY_SYSTEM, "Could not allocate icon memory");
+        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Could not allocate icon memory");
         return NULL;
     }
     for (int y = 0; y < height; ++y) {