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/CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.16)
 
-set(BOARD_COMPONENTS tactility-esp)
+set(BOARD_COMPONENTS tactility)
 
 if("${IDF_TARGET}" STREQUAL "esp32")
     list(APPEND BOARD_COMPONENTS
@@ -22,7 +22,3 @@ idf_component_register(
         "src/hello_world"
     REQUIRES ${BOARD_COMPONENTS}
 )
-
-# TODO Remove?
-target_link_libraries(${COMPONENT_LIB} ${IDF_TARGET_NAME} tactility)
-