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/Source/app/boot/Boot.cpp

@@ -10,6 +10,7 @@
 #include "lvgl.h"
 #include "Tactility.h"
 #include "hal/usb/Usb.h"
+#include "kernel/SystemEvents.h"
 
 #ifdef ESP_PLATFORM
 #include "kernel/PanicHandler.h"
@@ -35,6 +36,8 @@ struct Data {
 static int32_t bootThreadCallback(TT_UNUSED void* context) {
     TickType_t start_time = kernel::getTicks();
 
+    kernel::systemEventPublish(kernel::SystemEvent::BootSplash);
+
     auto* lvgl_display = lv_display_get_default();
     tt_assert(lvgl_display != nullptr);
     auto* hal_display = (hal::Display*)lv_display_get_user_data(lvgl_display);