Icons tweaked #4469

- The "light" icon theme is now a little lighter, to increase contrast.
- Toolbox icons are now small.
- Buttons:
  - Buttons without labels which use icons as their only source of info regarding what the button does (e.g. the white-balance pipette button) use normal-sized icons.
  - Labeled buttons which use icons as an auxiliary source of information (e.g. Auto-Crop) now use small icons. Curve type icons are also small even though they have no labels.
- Colored circles are smaller.
- Curve type icons redesigned and small.
- Hand icons (when panning the preview) redesigned to have a clear outline regardless of background color.
- Magnifier icons redesigned to have a thinner magnifier frame and larger inner parts.
- Perspective, distortion and crop icons redesigned.
- Some small icons were missing the `-small` suffix, now renamed.

rtdata/images/themed/svg/flip-horizontal.svg

@@ -27,7 +27,7 @@
      inkscape:pageopacity="0"
      inkscape:pageshadow="2"
      inkscape:zoom="34.25"
-     inkscape:cx="12"
+     inkscape:cx="7.7372263"
      inkscape:cy="12"
      inkscape:document-units="px"
      inkscape:current-layer="layer1"
@@ -135,7 +135,7 @@
        id="path2866"
        inkscape:connector-curvature="0" />
     <path
-       style="opacity:0.9;fill:none;fill-opacity:1;fill-rule:nonzero;stroke:#2a7fff;stroke-width:3;stroke-linecap:butt;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1;paint-order:normal"
+       style="opacity:0.7;fill:none;fill-opacity:1;fill-rule:nonzero;stroke:#2a7fff;stroke-width:3;stroke-linecap:butt;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1;paint-order:normal"
        d="M 19 10 A 7 7 0 0 1 19 10 L 19 10 L 19 10 A 7 7 0 0 1 12 17 A 7 7 0 0 1 5 10 "
        id="path859" />
     <path