dash: use vector logo and minimize SVGs

[vszakats]

Total size of 110 files (in bytes):

• original: 8.629.433
• original + brotli: 1.644.392
• original + svgo: 4.519.464
• original + svgo + brotli: 1.408.644
  →
• with SVG logo: 7.180.631
• with SVG logo + scour (4 decimals) 3x: 3.160.999
• with SVG logo + scour (4 decimals) 3x + svgo: 2.568.221
• with SVG logo + scour (4 decimals) 3x + svgo + brotli: 299.079

TL;DR size reduction is 2.7x (scour) to 3.4x (scour + svgo).

Notes:

• scour with 3 decimals is too lossy.
• svgo requires npm.
• both scour and svgo are optional and used automatically if present.

---

• test integration
• install an SVG minimizer, whichever is the most practical. svgo (needs nodejs), scour (pip, available as Debian package). → on the server
  svgcleaner does not work with these files.
• try minify tool [generic minimizer, with less gain than specialized SVG tools]
• maybe retrofit the output of this, incl minimization, to curl-everything's two SVGs

---

• original: 6.647.440
• original + brotli: 1.265.767
• original + svgo: 3.491.231
• original + svgo + brotli: 1.088.796
• ==
• with SVG logo: 5.580.543
• with SVG logo + minify: 4.944.735
• with SVG logo + scour (decimals 4): 2.621.618
• with SVG logo + scour (decimals 4) 2x: 2.560.658
• with SVG logo + scour (decimals 4) 3x: 2.557.784
• with SVG logo + scour (decimals 4) 3x + svgo: 2.077.884
• with SVG logo + scour (decimals 4) 3x + svgo + brotli: 268.125
• with SVG logo + scour (decimals 3): 2.489.792
• with SVG logo + scour (decimals 3) + svgo: 1.964.138
• with SVG logo + scour (decimals 3) + svgo + brotli: 246.824
• with SVG logo + scour (decimals 3) 2x: 2.428.384
• with SVG logo + scour (decimals 3) 2x + svgo: 1.977.707
• with SVG logo + scour (decimals 3) 2x + svgo + brotli: 246.340
• with SVG logo + svgo: 2.417.658
• with SVG logo + svgo + brotli: 302.086

[vszakats]

This is ready to merge. For best effect apt-get install scour needs
to be run on the server, and optionally npm install -g svgo too.