Refactor: render URL as property of MarketplacePortletDefinition.

Moves responsibility for computing render URL of defined portlet into `MarketplacePortletDefinition`, from portlet JSPs.
Adds utility method to `PortalWebUtils` to get request context.
Drops deepLink from model in favor of the renderUrl property of the `MarketplacePortletDefinition`.
Use MarketplacePortletDefinition renderUrl in servlet views.
Improve getRenderUrl JavaDoc.
Refactor: zap stray local variable, mark final.
Enable link to entry from Marketplace listing.
Related portlets are MarketplacePortletDefinitions.

Instead of `IPortletDefinition`s.
Related portlets link to their entries.
Trivial: Specify type of category set members.
Refactor: move featured portlet determination to service layer.
Trivial: fix saveRating JavaDoc.
Add featuredPortlets to Marketplace Servlet.
Merge pull request #318 from apetro/marketplace_servlet_links

Enable some servlet Marketplace links