Review caching implementation

Problem/Motivation

Caching in this module should be reviewed and checked to ensure it works as expected.
I guess it the cache needs to be cleared if the view is saved (cache tag). Perhaps the best would be to "inherit" the cache tags from the view, to not re-invent the same thing (which might be impossible).

And it should just behave like the views filter form!

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes