Disable JavaScript for MSIE6 users, update tests accordingly

MSIE6 is outdated and unsupported and has several unpatched security
vulnerabilities. [1] Its usage is strongly discouraged by Microsoft. [2]
Supporting its JavaScript engine requires significant testing and
development effort which is better spent elsewhere.

This effectively demotes MSIE6 to "Grade C" status per the MediaWiki
browser compatibility standards. [3]

This commit also labels the startup tests as "grade C" consistent with
the browser compatibility guidelines.

[1] http://secunia.com/advisories/product/11/
[2] https://www.modern.ie/en-us/ie6countdown
[3] https://www.mediawiki.org/wiki/Compatibility#Grade_C

Change-Id: I98140491ee980f65eac782b00c478f4f5c3a47fb
Merge "Disable JavaScript for MSIE6 users, update tests accordingly"