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/kernel/SystemEvents.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <cstdint>
+
+namespace tt::kernel {
+
+enum class SystemEvent {
+    BootInitHalBegin,
+    BootInitHalEnd,
+    BootInitI2cBegin,
+    BootInitI2cEnd,
+    BootInitLvglBegin,
+    BootInitLvglEnd,
+    BootSplash,
+    /** Gained IP address */
+    NetworkConnected,
+    NetworkDisconnected,
+    /** An important system time-related event, such as NTP update or time-zone change */
+    Time,
+};
+
+/** Value 0 mean "no subscription" */
+typedef uint32_t SystemEventSubscription;
+
+typedef void (*OnSystemEvent)(SystemEvent event);
+
+void systemEventPublish(SystemEvent event);
+SystemEventSubscription systemEventAddListener(SystemEvent event, OnSystemEvent handler);
+void systemEventRemoveListener(SystemEventSubscription subscription);
+
+}