Blog RSS doesn't work anymore when specifying a category

API breakage introduced in https://extensions.xwiki.org/xwiki/bin/view/Extension/Blog%20Application#Hv9.15 (BLOG-232)
At least one issue identified:
The CategoryRss page's "category" param is different since version 9.15, from https://www.xwiki.org/xwiki/bin/view/Blog/CategoryRss?xpage=plain&category=Blog.What%27s+New+for+XWiki to https://www.xwiki.org/xwiki/bin/view/Blog/CategoryRss?xpage=plain&category=Blog.Categories.What%27s+New+for+XWiki

A proper fix would provide support for both the old (Blog) and new (Blog.Categories) locations.
Additionally, the category migrator should be optional, with the posibility to disable the migration notification, and to provide extra information about the consequences of migrating a category in the new location.