Statusbar improvements (#36)

- Added sdcard service: it updates a statusbar icon and it can auto-unmount sdcards that were physically ejected by the user.
- Added `is_mounted` check for sdcard drivers
- Refactored assets: moved them from `tactility-esp/` to `data/`
- Made assets work with sim build
- Refactored wifi statusbar icons
- Refactored wifi_manage app access point icons
- Support not having an initial image icon when registering a new icon in statusbars. When a statusbar icon is added, it is now visible/invisible depending on whether an image was specified.
- Keep track of app memory on app start to find memory leaks (needs fine-tuning in the future)
- `tt_init()` assigns `config_instance` earlier, so it can be used during service init

tactility-esp/src/services/wifi/wifi.h

@@ -62,6 +62,9 @@ WifiRadioState wifi_get_radio_state();
  */
 void wifi_scan();
 
+/**
+ * @return true if wifi is actively scanning
+ */
 bool wifi_is_scanning();
 
 /**
@@ -96,6 +99,14 @@ void wifi_connect(const char* ssid, const char _Nullable password[64]);
  */
 void wifi_disconnect();
 
+/**
+ * Return the relevant icon asset from assets.h for the given inputs
+ * @param rssi the rssi value
+ * @param secured whether the access point is a secured one (as in: not an open one)
+ * @return
+ */
+const char* wifi_get_status_icon_for_rssi(int rssi, bool secured);
+
 #ifdef __cplusplus
 }
 #endif