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.

Added build phase scripts for automating running GruntJS and
retrieving latest styles.css, preview.css and abusefilter.css from
MobileApp extension for builds.

Change-Id: I86c42d62e4a02d4a7f653d6f325f5bc43adeade5