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/curve-nurbs.svg

@@ -26,7 +26,7 @@
      borderopacity="1.0"
      inkscape:pageopacity="0"
      inkscape:pageshadow="2"
-     inkscape:zoom="33.75"
+     inkscape:zoom="34.25"
      inkscape:cx="12"
      inkscape:cy="12"
      inkscape:document-units="px"
@@ -103,7 +103,7 @@
        id="g4919"
        transform="translate(-26.00658,-0.02511662)">
       <path
-         style="opacity:0.7;fill:none;fill-rule:evenodd;stroke:#2a7fff;stroke-width:2;stroke-linecap:butt;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1"
+         style="opacity:0.7;fill:none;fill-rule:evenodd;stroke:#2a7fff;stroke-width:2;stroke-linecap:round;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1"
          d="M 48,2.0000003 C 37.949603,6.1862437 31.908963,13.311815 28,22"
          id="path4882"
          inkscape:connector-curvature="0"