Update X-CS handling to new k/v pair spec

Per discussion between ops, mobile, and analytics, the X-CS HTTP
header is being repurposed as a general analytics header. Specific
data needed by analytics is serialized into key/value pairs that
are appended to the X-CS header, separated by ';'.

Also updates ncsa file to use X-Analytics rather than X-CS

Note that original X-CS handling is retained here, until we are certain
all upstream users of X-CS are updated, and that there are no other
issues with X-Analytics.

This is related to Change-Id: I93758fc76721d89f9c32a28c1821f3e59eb384ef

Change-Id: I14973cce2d2e80f480aabefa2dfbbfd5936db6cb
Merge "Update X-CS handling to new k/v pair spec" into production