Fixes for colours and margins in GPIO app and more (#284)

- Fixes for colours and margins in GPIO app
- Removed unused imports

Tactility/Source/lvgl/Color.cpp

@@ -0,0 +1,13 @@
+#include "Tactility/lvgl/Color.h"
+
+lv_color_t lv_color_foreground() {
+    return lv_color_make(0xFF, 0xFF, 0xFF);
+}
+
+lv_color_t lv_color_background() {
+    return lv_color_make(0x28, 0x2B, 0x30);
+}
+
+lv_color_t lv_color_background_darkest() {
+    return lv_color_make(0x00, 0x00, 0x00);
+}