list renderer: rewrite for speed
list renderer: rewrite for speed

Tests on Chrome 59.0.3071.109 x64 for Win:
* Old version using map+join: 2.xx seconds;
* The ECMAScript5 version with 2x loop unrolling: 160~180ms
* a simple ES5 version: 170~185ms
* replace the upper version with for-of: 190~210ms
* replace the upper version with const: 195~220ms

This commit chooses a version with shortest code,
because compilation target is ES5, so this version is not so bad.

gdh1995/vimium-plus,gdh1995/vimium-plus,gdh1995/vimium-plus