Moving some content hiding from server-side to CSS

This is a two part transition. First we will introduce the new CSS,
let people's old CSS caches expire, then we will remove the
corresponding HTML stripping code from MobileFrontend or the config

Change-Id: Ica45dfa10e6b510af13240ccf658172418b8ba26
Merge "Moving some content hiding from server-side to CSS"