Project restructuring: add tactility-headless (#55)

- Created `tactility-headless` to support ESP32 firmwares that don't require graphics
- `tactility` subproject now contains both PC and ESP32 code (to avoid having to split up `tactility` and `tactility-headless` into separate projects, which would result in a very complex dependency tree)
- `tactility` subproject is now defined as component for ESP32 and as regular module for PC
- Improvements for dispatcher
- Added `project-structure.puml` to docs
- `Gui` service now depends on `Loader` service instead of the reverse
- Added `statusbar_updater` service for updating Wi-Fi and SD card icons

tactility-headless/src/esp_partitions.h

@@ -0,0 +1,12 @@
+#pragma once
+
+#ifdef ESP_TARGET
+
+#include "esp_err.h"
+
+#define MOUNT_POINT_ASSETS "/assets"
+#define MOUNT_POINT_CONFIG "/config"
+
+esp_err_t tt_esp_partitions_init();
+
+#endif // ESP_TARGET