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

app-esp/src/main.c

@@ -1,16 +1,11 @@
 #include "board_config.h"
-#include "tactility_esp.h"
 
 // Apps
 #include "hello_world/hello_world.h"
+#include "tactility.h"
 
 extern void wifi_main(void*);
 
-extern const ServiceManifest wifi_service;
-extern const AppManifest gpio_app;
-extern const AppManifest wifi_connect_app;
-extern const AppManifest wifi_manage_app;
-
 void app_main(void) {
     static const Config config = {
         /**
@@ -19,19 +14,12 @@ void app_main(void) {
          */
         .hardware = TT_BOARD_HARDWARE,
         .apps = {
-            &gpio_app,
             &hello_world_app,
-            &wifi_connect_app,
-            &wifi_manage_app
-        },
-        .services = {
-            &wifi_service
         },
+        .services = {},
         .auto_start_app_id = NULL
     };
 
-    tt_esp_init();
-
     tt_init(&config);
 
     wifi_main(NULL);