GUI: Add missing flags + rework

Added missing flags
Resized to keep a coherent look
Replaced complex flags with simpler versions

default/icons/flags/ca.svg

@@ -0,0 +1,49 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   viewBox="0 0 32.4 21.6"
+   width="900"
+   height="600"
+   version="1.1"
+   id="svg6"
+   sodipodi:docname="ca.svg"
+   inkscape:version="1.1.1 (3bf5ae0d25, 2021-09-20)"
+   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="defs10" />
+  <sodipodi:namedview
+     id="namedview8"
+     pagecolor="#ffffff"
+     bordercolor="#666666"
+     borderopacity="1.0"
+     inkscape:pageshadow="2"
+     inkscape:pageopacity="0.0"
+     inkscape:pagecheckerboard="0"
+     showgrid="false"
+     width="749px"
+     inkscape:snap-page="true"
+     inkscape:zoom="0.49874598"
+     inkscape:cx="171.42995"
+     inkscape:cy="137.34446"
+     inkscape:window-width="1920"
+     inkscape:window-height="1017"
+     inkscape:window-x="-8"
+     inkscape:window-y="-8"
+     inkscape:window-maximized="1"
+     inkscape:current-layer="svg6" />
+  <rect
+     fill="#fcdd09"
+     width="32.400002"
+     height="21.6"
+     id="rect2"
+     x="0"
+     y="0"
+     style="stroke-width:1.2" />
+  <path
+     fill="#da121a"
+     d="m 32.4,12 v 2.4 H 0 V 12 Z M 4.608e-7,2.4 H 32.4 V 4.8 H 4.608e-7 Z m 0,4.8 H 32.4 V 9.6 H 4.608e-7 Z M 0,16.8 h 32.4 v 2.4 H 0 Z"
+     id="path4"
+     style="stroke-width:1.2" />
+</svg>