Improve cache invalidation, deleting relations, and reindexing

[sebbacon]

Renaming of a body, or changing its domain, should clear the cached bubbles of
all requests to that body.

Destroying an info_request doesn't remove corresponding tags: the fully_destroy method iterates over related events, logs, etc and removes them, but doesn't do the same for tags.

Other references to title field changes don't get search index updated when title is altered (e.g. when a public body is renamed).

We currently never update cached attachment text unless cache is explicitly cleared (which might matter with software updates, or code changes). Embed some identifier in the code and the cache directory, thus detect changes and automatically clear the cache.

[crowbot]

See also #1475

[crowbot]

This is an old collection of different concerns. Closing it - please re-open specific tickets for any of these issues if you can replicate them.