Add unit tests for buttons / relays; and a bunch of mocks :)

unittest/main.c

@@ -3,10 +3,15 @@
 int test_failures=0;
 int assert_count=0;
 
+uint32_t mqtt_pub_count;
+uint32_t mqtt_sub_count;
+
 int main() {
   test_widget();
   test_widget_mqtt();
   test_screen();
+  test_buttons();
+  test_relays();
 
   if (test_failures) {
     LOG(LL_ERROR, ("%d test failures", test_failures));