Regression: fix hamburger and left menu icon alignment

Hamburger in beta and left menu icons in stable were not aligned
properly on iOS (< 7, maybe early 7 too) and Android 2.x because four
value background-position is not supported there.

Use percent values instead, CSSJanus seems to be changing them fine for
RTL languages.

Change-Id: Iaee44d2b67c419efe5f841219b3fd652f1e69cf4
Merge "Regression: fix hamburger and left menu icon alignment"