Sync with MobileApp extension css.

Consolidated DownloadLeadSectionOp.m and DownloadNonLeadSectionsOp.m
into single DownloadSectionsOp.m

Now periodically syncs styles.css, preview.css and abusefilter.css.

Note: not presently using abusefilter.css or abusefilter.html in
anticipation of potentially forthcoming native designs for handling
abuse filter messages.

Change-Id: I86c42d62e4a02d4a7f653d6f325f5bc43adeade5