Correct help page CSS issues (fixes #1479)
- https://aspnetwebstack.codeplex.com/workitem/1479
- "Help page font flickers on navigating to service url or help page home"
- Problems arise due to lousy HelpPage.css link placement and application of
help page styles to site banner and footer
- Scope styles in HelpPage.css to elements beneath one with the help-page
(or existing help-page-table) class
- Correct HelpPage.css style for the <body/> element to apply to the
<div id="body"/> element in all three help page views
- Move HelpPage.css link to the top of the help page views, avoiding current
placement at the bottom of the page when using application layout
- Use help-page class at top of the help page views

(cherry picked from commit 1fe1c1a57a7b1555f786d3f61a4414c15d15b54a)