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)

Data/system_sources/app_icon_time_date_settings.svg

@@ -0,0 +1,42 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   height="16"
+   viewBox="0 -960 640 640"
+   width="16"
+   fill="#e8eaed"
+   version="1.1"
+   id="svg1"
+   sodipodi:docname="calendar_clock_24dp_E8EAED_FILL0_wght400_GRAD0_opsz24.svg"
+   inkscape:export-filename="calendar_clock_24dp_E8EAED_FILL0_wght400_GRAD0_opsz24.png"
+   inkscape:export-xdpi="96.18351"
+   inkscape:export-ydpi="96.18351"
+   inkscape:version="1.4 (e7c3feb100, 2024-10-09)"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:svg="http://www.w3.org/2000/svg">
+  <defs
+     id="defs1" />
+  <sodipodi:namedview
+     id="namedview1"
+     pagecolor="#505050"
+     bordercolor="#eeeeee"
+     borderopacity="1"
+     inkscape:showpageshadow="0"
+     inkscape:pageopacity="0"
+     inkscape:pagecheckerboard="0"
+     inkscape:deskcolor="#d1d1d1"
+     inkscape:zoom="47.5"
+     inkscape:cx="10.842105"
+     inkscape:cy="10.821053"
+     inkscape:window-width="2560"
+     inkscape:window-height="1368"
+     inkscape:window-x="0"
+     inkscape:window-y="0"
+     inkscape:window-maximized="1"
+     inkscape:current-layer="svg1" />
+  <path
+     d="M 61.257143,-775.80752 H 487.10977 v -60.83609 H 61.257143 Z m 0,0 v -60.83609 z m 0,425.85263 q -25.094888,0 -42.965489,-17.8706 -17.870601,-17.8706 -17.870601,-42.96549 v -425.85263 q 0,-25.09489 17.870601,-42.96549 17.870601,-17.8706 42.965489,-17.8706 H 91.67518 v -60.83609 h 60.83609 v 60.83609 h 243.34437 v -60.83609 h 60.83609 v 60.83609 h 30.41804 q 25.09489,0 42.96549,17.8706 17.8706,17.8706 17.8706,42.96549 v 172.62241 q -14.44857,-6.84406 -29.6576,-11.40677 -15.20901,-4.56271 -31.17849,-6.84406 v -32.6994 H 61.257143 v 304.18045 H 252.89083 q 5.32315,16.72993 12.54744,31.93895 7.22428,15.20902 17.11015,28.89714 z m 395.434587,30.41805 q -63.11745,0 -107.60384,-44.48639 -44.48639,-44.4864 -44.48639,-107.60384 0,-63.11744 44.48639,-107.60384 44.48639,-44.48638 107.60384,-44.48638 63.11744,0 107.60383,44.48638 44.48639,44.4864 44.48639,107.60384 0,63.11744 -44.48639,107.60384 -44.48639,44.48639 -107.60383,44.48639 z m 50.95022,-79.84737 21.29264,-21.29263 -57.03384,-57.03384 V -562.8812 H 441.4827 v 97.33774 z"
+     id="path1"
+     style="stroke-width:0.760454;fill:#000000" />
+</svg>