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)

Boards/LilygoTdeck/Source/hal/TdeckDisplayConstants.h

@@ -4,7 +4,7 @@
 #define TDECK_LCD_PIN_CS GPIO_NUM_12
 #define TDECK_LCD_PIN_DC GPIO_NUM_11 // RS
 #define TDECK_LCD_PIN_BACKLIGHT GPIO_NUM_42
-#define TDECK_LCD_SPI_FREQUENCY 40000000
+#define TDECK_LCD_SPI_FREQUENCY 80000000
 #define TDECK_LCD_HORIZONTAL_RESOLUTION 320
 #define TDECK_LCD_VERTICAL_RESOLUTION 240
 #define TDECK_LCD_BITS_PER_PIXEL 16