Add tests covering how blog, post and category locations are resolved

Preparation for moving the logic that decides where a blog's posts and categories live out of the wiki pages and into Java code.

That logic is currently spread over many pages (Blog.BlogCode, Blog.BlogParameters, Blog.BlogPostList, Blog.CategoriesCode, Blog.ManageCategories, Blog.Management, Blog.CreatePost, Blog.BlogPostSheet, the categories and related blogs panels, Blog.CategoryRss) and the Java listeners and migration (BlogMoveListener, CategoryRenameListener, CategoryLocationMigration). Most of it is only covered indirectly by functional tests, if at all.

Scope

• Characterization tests pinning the current behaviour (including known bugs, which get their own issues) for:
  • the default blog with categories in Blog.Categories and in the legacy Blog space,
  • a blog in its own space, a blog with custom posts and categories locations, a blog stored as Space.Blog, a blog whose name contains special characters,
  • moving a blog, moving its categories space alone, creating, renaming and deleting categories, creating posts.
• Java unit tests for CategoryRenameListener and CategoryLocationMigration, more cases for BlogMoveListener.
• Page tests for the rules that don't depend on queries; functional (Docker) tests for the ones that do.

No change in behaviour.