Time & date, system events and much more (#152)

## Time & Date
- Added time to statusbar widget
- Added Time & Date Settings app
- Added TimeZone app for selecting TimeZone
- Added `tt::time` namespace with timezone code

## Other changes

- Added `SystemEvent` to publish/subscribe to system wide (e.g. for init code, but also for time settings changes)
- Changed the way the statusbar widget works: now there's only 1 that gets shown/hidden, instead of 1 instance per app instance.
- Moved `lowercase()` function to new namespace: `tt::string`
- Increased T-Deck flash & PSRAM SPI frequencies to 120 MHz (from 80 MHz)
- Temporary work-around (+ TODO item) for LVGL stack size (issue with WiFi app)
- Suppress T-Deck keystroke debugging to debug level (privacy issue)
- Improved SDL dependency wiring in various `CMakeLists.txt`
- `Loader` service had some variables renamed to the newer C++ style (from previous C style)

Tactility/Private/service/gui/Gui_i.h

@@ -23,13 +23,14 @@ struct Gui {
     PubSubSubscription* loader_pubsub_subscription = nullptr;
 
     // Layers and Canvas
-    lv_obj_t* lvgl_parent = nullptr;
+    lv_obj_t* appRootWidget = nullptr;
+    lv_obj_t* statusbarWidget = nullptr;
 
     // App-specific
-    ViewPort* app_view_port = nullptr;
+    ViewPort* appViewPort = nullptr;
 
     lv_obj_t* _Nullable keyboard = nullptr;
-    lv_group_t* keyboard_group = nullptr;
+    lv_group_t* keyboardGroup = nullptr;
 };
 
 /** Update GUI, request redraw */