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/Tactility.cpp

@@ -54,6 +54,8 @@ namespace app {
     namespace settings { extern const AppManifest manifest; }
     namespace systeminfo { extern const AppManifest manifest; }
     namespace textviewer { extern const AppManifest manifest; }
+    namespace timedatesettings { extern const AppManifest manifest; }
+    namespace timezone { extern const AppManifest manifest; }
     namespace usbsettings { extern const AppManifest manifest; }
     namespace wifiapsettings { extern const AppManifest manifest; }
     namespace wificonnect { extern const AppManifest manifest; }
@@ -87,6 +89,8 @@ static const std::vector<const app::AppManifest*> system_apps = {
     &app::selectiondialog::manifest,
     &app::systeminfo::manifest,
     &app::textviewer::manifest,
+    &app::timedatesettings::manifest,
+    &app::timezone::manifest,
     &app::usbsettings::manifest,
     &app::wifiapsettings::manifest,
     &app::wificonnect::manifest,