Cache tags based cache revalidation

[lauriii]

The current cache revalidation is purely based on paths. This doesn't take into account lists, and can easily lead to issues with scaling because updating an entity could easily require revalidating hundreds, if not thousands of pages.

We should look into implementing a cache tags based revalidation logic.

[fiasco]

Suggest this issue is renamed to just "cache tag invalidation" since I think thats the feature we want here. Once its provided, we can add support to the CMS by integrating with the Purge module (not Acquia Purge).