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)

TactilityHeadless/Source/hal/Configuration.h

@@ -10,8 +10,6 @@ typedef bool (*InitBoot)();
 typedef bool (*InitHardware)();
 typedef bool (*InitLvgl)();
 
-typedef void (*SetBacklightDuty)(uint8_t);
-
 class Display;
 class Keyboard;
 typedef Display* (*CreateDisplay)();
@@ -57,7 +55,7 @@ struct Configuration {
     const CreatePower _Nullable power = nullptr;
 
     /**
-     * A list of i2c devices (can be empty, but preferably accurately represents the device capabilities)
+     * A list of i2c interfaces
      */
     const std::vector<i2c::Configuration> i2c = {};
 };