Finish display impl, write UI widget, refactor

main/ui.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include "lvgl.h"
+
+#include "motor.h"
+
+/** Numberstack button callback type */
+typedef void (*ns_btn_cb_t)(lv_event_t *);
+
+typedef struct {
+    ns_btn_cb_t top_cb;
+    ns_btn_cb_t bottom_cb;
+} ns_widget_ctx_t; /** Numberstack widget context type */
+
+void build_numberstack(lv_obj_t * parent,
+        const char * label_text,
+        lv_obj_t ** label_value,
+        ns_btn_cb_t top_btn_cb,
+        ns_btn_cb_t bottom_btn_cb);
+
+void build_ui(void);