Further losslessly compress images

 * apple-touch-icon-precomposed.png

   before:         3962 B
   after:          3959 B
   ──────────────────────
   reduction:         3 B [0.07%]

 * tile.png

   before:         3495 B
   after:          3482 B
   ──────────────────────
   reduction:        13 B [0.37%]

 * tile-wide.png

   before:         1864 B
   after:          1854 B
   ──────────────────────
   reduction:        10 B [0.53%]
Make consistency changes in `test/tests.js`
Add `test/tests.js` in the JSHint check