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.cpp

@@ -0,0 +1,87 @@
+#include "SystemEvents.h"
+#include "Mutex.h"
+#include "CoreExtraDefines.h"
+#include <list>
+
+#define TAG "system_event"
+
+namespace tt::kernel {
+
+struct SubscriptionData {
+    SystemEventSubscription id;
+    SystemEvent event;
+    OnSystemEvent handler;
+};
+
+static Mutex mutex;
+static SystemEventSubscription subscriptionCounter = 0;
+static std::list<SubscriptionData> subscriptions;
+
+static const char* getEventName(SystemEvent event) {
+    switch (event) {
+        case SystemEvent::BootInitHalBegin:
+            return TT_STRINGIFY(SystemEvent::BootInitHalBegin);
+        case SystemEvent::BootInitHalEnd:
+            return TT_STRINGIFY(SystemEvent::BootInitHalEnd);
+        case SystemEvent::BootInitI2cBegin:
+            return TT_STRINGIFY(SystemEvent::BootInitI2cBegin);
+        case SystemEvent::BootInitI2cEnd:
+            return TT_STRINGIFY(SystemEvent::BootInitI2cEnd);
+        case SystemEvent::BootInitLvglBegin:
+            return TT_STRINGIFY(SystemEvent::BootInitLvglBegin);
+        case SystemEvent::BootInitLvglEnd:
+            return TT_STRINGIFY(SystemEvent::BootInitLvglEnd);
+        case SystemEvent::BootSplash:
+            return TT_STRINGIFY(SystemEvent::BootSplash);
+        case SystemEvent::NetworkConnected:
+            return TT_STRINGIFY(SystemEvent::NetworkConnected);
+        case SystemEvent::NetworkDisconnected:
+            return TT_STRINGIFY(SystemEvent::NetworkDisconnected);
+        case SystemEvent::Time:
+            return TT_STRINGIFY(SystemEvent::Time);
+    }
+
+    tt_crash(); // Missing case above
+}
+
+void systemEventPublish(SystemEvent event) {
+    TT_LOG_I(TAG, "%s", getEventName(event));
+
+    if (mutex.lock(portMAX_DELAY)) {
+        for (auto& subscription : subscriptions) {
+            if (subscription.event == event) {
+                subscription.handler(event);
+            }
+        }
+
+        mutex.unlock();
+    }
+}
+
+SystemEventSubscription systemEventAddListener(SystemEvent event, OnSystemEvent handler) {
+    if (mutex.lock(portMAX_DELAY)) {
+        auto id = ++subscriptionCounter;
+
+        subscriptions.push_back({
+            .id = id,
+            .event = event,
+            .handler = handler
+        });
+
+        mutex.unlock();
+        return id;
+    } else {
+        tt_crash();
+    }
+}
+
+void systemEventRemoveListener(SystemEventSubscription subscription) {
+    if (mutex.lock(portMAX_DELAY)) {
+        std::erase_if(subscriptions, [subscription](auto& item) {
+            return (item.id == subscription);
+        });
+        mutex.unlock();
+    }
+}
+
+}